記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-023-36188-z

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/acd007

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その他リンク： https://iopscience.iop.org/article/10.3847/2041-8213/acd007/pdf

担当区分：筆頭著者   記述言語：英語   掲載種別：論文集(書籍)内論文  

DOI： 10.1007/978-981-19-7765-7_10

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stac2635

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2021JD035658

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JD035658

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac7395

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac7395/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41550-021-01459-0

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その他リンク： https://www.nature.com/articles/s41550-021-01459-0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-021-01530-0

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-021-01486-1

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abf3c1

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1186/s40623-021-01420-5

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

It is of great interest and importance to study the variabilities of solar EUV, UV and X-ray irradiance in heliophysics, in Earth's climate, and space weather applications. A careful study is required to identify, track, monitor and segment the different coronal features such as active regions (ARs), coronal holes (CHs), the background regions (BGs) and the X-ray bright points (XBPs) from spatially resolved full-disk images of the Sun. Variability of solar soft X-ray irradiance is studied for a period of 13 years (February 2007-March 2020, covers Solar Cycle 24), using the X-Ray Telescope on board the Hinode (Hinode/XRT) and GOES (1 - 8 angstrom). The full-disk X-ray images observed in Al_mesh filter from XRT are used, for the first time, to understand the solar X-ray irradiance variability measured, Sun as a star, by GOES instrument. An algorithm in Python has been developed and applied to identify and segment coronal X-ray features (ARs, CHs, BGs, and XBPs) from the full-disk soft X-ray observations of Hinode/XRT. The segmentation process has been carried out automatically based on the intensity level, morphology and sizes of the X-ray features. The total intensity, area, and contribution of ARs/CHs/BGs/XBPs features were estimated and compared with the full-disk integrated intensity (FDI) and GOES (1 - 8 angstrom) X-ray irradiance measurements. The XBPs have been identified and counted automatically over the full disk to investigate their relation to solar magnetic cycle. The total intensity of ARs/CHs/BGs/XBPs/FD regions are compared with the GOES (1 - 8 angstrom) X-ray irradiance variations. We present the results obtained from Hinode/XRT full-disk images (in Al_mesh filter) and compare the resulting integrated full-disk intensity (FDI) with GOES X-ray irradiance. The X-ray intensity measured over ARs/CHs/BGs/XBPs/FD is well correlated with GOES X-ray flux. The contributions of the segmented X-ray features to FDI and X-ray irradiance variations are determined. It is found that the background and active regions have a greater impact on the X-ray irradiance fluctuations. The mean contribution estimated for the whole observed period of the background regions (BGs) will be around 65 +/- 10.97%, whereas the ARs, XBPs and CHs are 30 +/- 11.82%, 4 +/- 1.18% and 1 +/- 0.52%, respectively, to total solar X-ray flux. We observed that the area and contribution of ARs and CHs varies with the phase of the solar cycle, whereas the BGs and XBPs show an anti-correlation. We find that the area of the coronal features is highly variable suggesting that their area has to be taken into account in irradiance models, in addition to their intensity variations. The time series results of XBPs suggest for an existence of anti-correlation between the number of XBPs and the sunspot numbers. It is also important to consider both the number variation and the contribution of XBPs in the reconstruction of total solar X-ray irradiance variability.

DOI： 10.1007/s11207-021-01785-6

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abea13

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abe414

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevE.102.060201

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abbb93

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abb60e

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aba61a

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab822c

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4365/ab64f2

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab65f0

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab6bc8

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2514-3433/ab404ach2

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab5582

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society This is an erratum to the paper 'Supergranular turbulence in the quiet Sun: Lagrangian coherent structures' that was published in MNRAS, 488, 3076-3088 (2019). In the original version of stz1909, there were several instances where the author's corrections had not been implemented during the proofing stages. These have now been corrected as follows: (i) Page 3077: in the second paragraph, the reference 'G16 G17' has been corrected to 'Gošić et al. 2014, 2016'. (ii) Page 3079: in section 3.1, the reference 'G20' has been corrected to 'Haller (2015)'. (iii) Page 3087: the article ID 'eeau2307' has been added to reference 'Hotta H., Iijima H., Kusano K., 2019, Sci. Adv., 5'. The publisher apologises for these errors.

DOI： 10.1093/mnras/stz2296

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stz1909

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab2e11

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4365/ab2e12

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5084771

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/201834031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1126/sciadv.aau2307

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jastp.2017.08.035

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aad181

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aac5e1

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.pss.2017.12.016

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aaacd1

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41467-017-02616-8

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Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

© ESO, 2017. Aims. We report the small temporal variation of the axial dipole moment near the solar minimum and its application to the solar-cycle prediction by the surface flux transport (SFT) model. Methods. We measure the axial dipole moment using the photospheric synoptic magnetogram observed by the Wilcox Solar Observatory (WSO), the ESA/NASA Solar and Heliospheric Observatory Michelson Doppler Imager (MDI), and the NASA Solar Dynamics Observatory Helioseismic and Magnetic Imager (HMI). We also use the SFT model for the interpretation and prediction of the observed axial dipole moment. Results. We find that the observed axial dipole moment becomes approximately constant during the period of several years before each cycle minimum, which we call the axial dipole moment plateau. The cross-equatorial magnetic flux transport is found to be small during the period, although a significant number of sunspots are still emerging. The results indicate that the newly emerged magnetic flux does not contribute to the build up of the axial dipole moment near the end of each cycle. This is confirmed by showing that the time variation of the observed axial dipole moment agrees well with that predicted by the SFT model without introducing new emergence of magnetic flux. These results allow us to predict the axial dipole moment at the Cycle 24/25 minimum using the SFT model without introducing new flux emergence. The predicted axial dipole moment at the Cycle 24/25 minimum is 60-80 percent of Cycle 23/24 minimum, which suggests the amplitude of Cycle 25 is even weaker than the current Cycle 24. Conclusions. The plateau of the solar axial dipole moment is an important feature for the longer-term prediction of the solar cycle based on the SFT model.

DOI： 10.1051/0004-6361/201731813

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4996982

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa799b

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa750e

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa6dfe

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41550-017-0085

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa6682

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41550-017-0085

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/835/1/84

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本航空宇宙学会  

<p>太陽活動に起因した太陽地球圏環境の変動は，人類の宇宙活動のみならず，電力・通信・測位システムなど現代社会の様々な基盤にも大きな影響を与える．また，太陽周期活動の変化は長期的な気候変動にも影響を与えることが考えられる．そうした太陽地球環境の変動を予測するために，これまで多くの努力がなされているが，未だに十分正確な予測技術を我々は獲得できていない．特に，従来の予測方法は過去の観測データに基づく経験的手法に依存しているため，科学的観測データが不足する大規模変動とその影響の予測には困難がある．また，太陽地球圏のダイナミクスは複合的現象であり，その理解のためには分野横断的な研究が不可欠となる．現在，我が国では多くの関連研究機関が協力し，新学術領域研究「太陽地球圏環境予測（PSTEP）」が進行中である．国内外の研究機関との協力研究を通して，今後，多くの成果が生まれることが期待される．</p>

DOI： 10.14822/kjsass.65.1_22

CiNii Books

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s11207-016-0923-0

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/0004-637X/818/2/168

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4934652

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4932079

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015SW001213

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_896

CiNii Books

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Understanding the mechanism that produces solar flares is important not only from the scientific point of view but also for improving space weather predictability. There are numerous observational and computational studies that have attempted to reveal the onset mechanism of solar flares. However, the underlying mechanism of flare onset remains elusive. To elucidate the flare trigger mechanism, we analyzed several flare events which were observed by Hinode/Solar Optical Telescope (SOT) in our previous study. Because of the limitation of the SOT field of view, however, only four events in the Hinode data sets have been usable. Therefore, increasing the number of events is required for evaluating the flare trigger models. We investigated the applicability of data obtained by the Solar Dynamics Observatory (SDO) to increase the data sample for a statistical analysis of the flare trigger process. SDO regularly observes the full disk of the sun and all flares, although its spatial resolution is lower than that of Hinode. We investigated the M6.6 flare which occurred on 2011 February 13, and compared the analyzed data of SDO with the results of our previous study using Hinode/SOT data. Filter and vector magnetograms obtained by the Helioseismic and Magnetic Imager and filtergrams from the Atmospheric Imaging Assembly (AIA) 1600 angstrom were employed. From the comparison of small-scale magnetic configurations and chromospheric emission prior to the flare onset, we confirmed that the trigger region is detectable with the SDO data. We also measured the magnetic shear angles of the active region and the azimuth and strength of the flare trigger field. The results were consistent with our previous study. We concluded that statistical studies of the flare trigger process are feasible with SDO as well as Hinode data. We also investigated the temporal evolution of the magnetic field before the flare onset with SDO.

DOI： 10.1093/pasj/psu091

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psu092

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psu092

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s11207-014-0502-1

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We develop a nonlinear force-free field (NLFFF) extrapolation code based on the magnetohydrodynamic (MHD) relaxation method. We extend the classical MHD relaxation method in two important ways. First, we introduce an algorithm initially proposed by Dedner et al. to effectively clean the numerical errors associated with del . B. Second, the multigrid type method is implemented in our NLFFF to perform direct analysis of the high-resolution magnetogram data. As a result of these two implementations, we successfully extrapolated the high resolution force-free field introduced by Low & Lou with better accuracy in a drastically shorter time. We also applied our extrapolation method to the MHD solution obtained from the flux-emergence simulation by Magara. We found that NLFFF extrapolation may be less effective for reproducing areas higher than a half-domain, where some magnetic loops are found in a state of continuous upward expansion. However, an inverse S-shaped structure consisting of the sheared and twisted loops formed in the lower region can be captured well through our NLFFF extrapolation method. We further discuss how well these sheared and twisted fields are reconstructed by estimating the magnetic topology and twist quantitatively.

DOI： 10.1088/0004-637X/780/1/101

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present a 2.5 dimensional magnetohydrodynamic simulation of a magnetic flux rope (FR) propagating in the heliosphere and investigate the cause of the observed sharp plasma beta transition. Specifically, we consider a strong internal magnetic field and an explosive fast start, such that the plasma beta is significantly lower in the FR than in the sheath region that is formed ahead. This leads to an unusual FR morphology in the first stage of propagation, while the more traditional view (e. g., from space weather simulations like Enlil) of a pancake-shaped FR is observed as it approaches 1 AU. We investigate how an equipartition line, defined by a magnetic Weber number, surrounding a core region of a propagating FR, can demarcate a boundary layer where there is a sharp transition in the plasma beta. The substructure affects the distribution of toroidal flux, with the majority of the flux remaining in a small core region that maintains a quasi-cylindrical structure. We quantitatively investigate a locus of points where the kinetic energy density of the relative inflow field is equal to the energy density of the transverse magnetic field (i.e., effective tension force). The simulation provides compelling evidence that at all heliocentric distances the distribution of toroidal magnetic flux away from the FR axis is not linear, with 80% of the toroidal flux occurring within 40% of the distance from the FR axis. Thus, our simulation displays evidence that the competing ideas of a pancaking structure observed remotely can coexist with a quasi-cylindrical magnetic structure seen in situ.

DOI： 10.1088/0004-637X/779/2/142

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To better understand a preferred magnetic field configuration and its evolution during coronal mass ejection (CME) events, we investigated the spatial and temporal evolution of photospheric magnetic fields in the active region NOAA 9236 that produced eight flare-associated CMEs during the time period of 2000 November 23-26. The time variations of the total magnetic helicity injection rate and the total unsigned magnetic flux are determined and examined not only in the entire active region but also in some local regions such as the main sunspots and the CME-associated flaring regions using SOHO/MDI magnetogram data. As a result, we found that (1) in the sunspots, a large amount of positive (right-handed) magnetic helicity was injected during most of the examined time period, (2) in the flare region, there was a continuous injection of negative (left-handed) magnetic helicity during the entire period, accompanied by a large increase of the unsigned magnetic flux, and (3) the flaring regions were mainly composed of emerging bipoles of magnetic fragments in which magnetic field lines have substantially favorable conditions for making reconnection with large-scale, overlying, and oppositely directed magnetic field lines connecting the main sunspots. These observational findings can also be well explained by some MHD numerical simulations for CME initiation (e. g., reconnection-favored emerging flux models). We therefore conclude that reconnection-favored magnetic fields in the flaring emerging flux regions play a crucial role in producing the multiple flare-associated CMEs in NOAA 9236.

DOI： 10.1088/0004-637X/778/1/13

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigated four major solar flare events that occurred in active regions NOAA 10930 (2006 December 13 and 14) and NOAA 11158 (2011 February 13 and 15) by using data observed by the Solar Optical Telescope on board the Hinode satellite. To reveal the trigger mechanism of solar flares, we analyzed the spatio-temporal correlation between the detailed magnetic field structure and the emission image of the Ca ii H line at the central part of flaring regions for several hours prior to the onset of the flares. In all the flare events, we observed that the magnetic shear angle in the flaring regions exceeded 70 degrees, as well as that characteristic magnetic disturbances developed at the centers of flaring regions in the pre-flare phase. These magnetic disturbances can be classified into two groups depending on the structure of their magnetic polarity inversion lines; the so-called opposite-polarity and reversed-shear magnetic field recently proposed by our group, although the magnetic disturbance in one event of the four samples is too subtle to clearly recognize the detailed structure. The result suggests that some major solar flares are triggered by rather small magnetic disturbances. We also show that the critical size of the flare-trigger field varies among flare events and briefly discuss how the flare-trigger process depends on the evolution of active regions.

DOI： 10.1088/0004-637X/778/1/48

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We consider transition to Hall-magnetohydrodynamics regimes of the resistive tearing instability in weakly ionized plasmas. A particular emphasis is put on a possible role of the resulting fast magnetic reconnection in such astrophysical objects as solar chromosphere, interstellar molecular clouds and protostellar discs. It is shown that Hall-mediated reconnection can be relevant to explosive phenomena in the latter, though it is unlikely to take place in the former two environments.

DOI： 10.1093/mnras/stt1155

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report a detailed event analysis of the M6.6 class flare in the active region (AR) NOAA 11158 on 2011 February 13. AR 11158, which consisted of two major emerging bipoles, showed prominent activity including one X- and several M-class flares. In order to investigate the magnetic structures related to the M6.6 event, particularly the formation process of a flare-triggering magnetic region, we analyzed multiple spacecraft observations and numerical results of a flare simulation. We observed that, in the center of this quadrupolar AR, a highly sheared polarity inversion line (PIL) was formed through proper motions of the major magnetic elements, which built a sheared coronal arcade lying over the PIL. The observations lend support to the interpretation that the target flare was triggered by a localized magnetic region that had an intrusive structure, namely, a positive polarity penetrating into a negative counterpart. The geometrical relationship between the sheared coronal arcade and the triggering region is consistent with the theoretical flare model based on the previous numerical study. We found that the formation of the trigger region was due to the continuous accumulation of small-scale magnetic patches. A few hours before the flare occurred, the series of emerged/advected patches reconnected with a pre-existing field. Finally, the abrupt flare eruption of the M6.6 event started around 17:30 UT. Our analysis suggests that in the process of triggering flare activity, all magnetic systems on multiple scales are included, not only the entire AR evolution but also the fine magnetic elements.

DOI： 10.1088/0004-637X/773/2/128

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/swe.20045

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4789449

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1253/circj.CJ-66-0054

Web of Science

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/760/1/31

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/759/2/103

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s11207-012-0041-6

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/752/2/126

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/747/2/130

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

In order to discuss the propagation of Alfven wave in the real solar atmosphere, we calculate three dimensional magnetic field using magnetic field observation obtained with Hinode and a high resolution potential field model. The modeled field reproduces fun out (canopy) structure rooted to patchy concentrations of magnetic flux (kG-patches) in the polar region. Combined with a atmosphere model, the model shows that most of the Alfven wave propagating along the magnetic field lines can hardly pass through the transition region due to reflection there. The model suggests that strong concentration of the magnetic field may make retardation of Alfven wave phase between neighboring field lines rooted on the edge of the canopy. The situation may be potential situation for Alfven wave dissipation due to phase mixing process.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

In this paper we report shear motions (3-5 km s(-1)) of magnetic elements observed at a preflare of an X3.4 flare (around 02:00 UT on 2006 December 13) in active region 10930. This preflare is observed by X-ray Telescope onboard Hinode. Velocity fields are obtained from filter magnetograms of the Solar Optical Telescope. We also analyzed velocity fields divided into divergent and rotation components. From these velocity components, two local twisting motions are found. One twisting motion continues for 0.5 hours, and another continues at least for 2.5 hours.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Twist and connectivity of magnetic field lines in the flare-productive active region NOAA 10930 are investigated in terms of the vector magnetograms observed by the Solar Optical Telescope on board the Hinode satellite and the nonlinear force-free field (NLFFF) extrapolation. First, we show that the footpoints of magnetic field lines reconstructed by the NLFFF correspond well to the conjugate pair of highly sheared flare ribbons on the Ca II images, which were observed by Hinode as an X3.4 class flare on 2006 December 13. This demonstrates that the NLFFF extrapolation may be used to analyze the magnetic field connectivity. Second, we find that the twist of magnetic field lines anchored on the flare ribbons increased as the ribbons moved away from the magnetic polarity inversion line in the early phase of the flare. This suggests that magnetic reconnection might commence from a region located below the most strongly twisted field. Third, we reveal that the magnetic flux twisted more than a half turn and gradually increased during the last one day prior to the onset of the flare, and that it quickly decreased for two hours after the flare. This is consistent with the store-and-release scenario of magnetic helicity. However, within this active region, only a small fraction of the flux was twisted by more than one full turn and the field lines that reconnected first were twisted less than one turn. These results imply that the kink mode instability could hardly occur, at least before the onset of flare. Based on our results, we discuss the trigger process of solar flares.

DOI： 10.1088/0004-637X/738/2/161

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2514/1.B34141

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/732/2/111

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/732/2/117

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/731/2/109

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Two mission concepts (plan A: out-of-ecliptic mission and plan B: high resolution spectroscopic mission) have been studied for the next Japanese-led solar mission Solar-C, which will follow the scientific success of the Hinode mission. The both mission concepts are concluded as equally important and attractive for the promotion of space solar physics. In the meantime we also had to make efforts for prioritizing the two options, in order to proceed to next stage of requesting the launch of Solar-C mission at the earliest opportunity. This paper briefly describes the two mission concepts and the current status on our efforts for prioritizing the two options. More details are also described for the plan B option as the first-priority Solar-C mission. The latest report from the Solar-C mission concept studies was documented as "Interim Report on the Solar-C Mission Concept."

DOI： 10.1117/12.893228

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Several divergence-cleaning techniques for multi-dimensional Godunov-type magnetohydrodynamic schemes are comparatively investigated. We also propose a new divergence-cleaning technique that is improved from an earlier projection method to improve the robustness. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.

DOI： 10.1585/pfr.6.2406124

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A magnetohydrodynamic (MHD) algorithm for global simulations of planetary magnetospheres is developed based on an approximate nonlinear Riemann solver, the so-called Harten-Lax-van Leer-Discontinuities (HLLD) approximate Riemann solver. An approximate nonlinear solution of the MHD Riemann problem, in which the contributions of the background potential magnetic field are subtracted and multispecies plasmas as well as general equation of state are included, can be algebraically obtained under the assumptions that the normal velocity and the background potential magnetic field in the Riemann fan are constant. The theoretical aspects of the HLLD approximate Riemann solver are focused on, in particular.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A magnetohydrodynamic (MHD) algorithm for global simulations of planetary magnetospheres is developed based on an approximate nonlinear Riemann solver, the so-called Harten-Lax-van Leer-Discontinuities (HLLD) approximate Riemann solver. An approximate nonlinear solution of the MHD Riemann problem, in which the contributions of the background potential magnetic field are subtracted and multispecies plasmas as well as general equation of state are included, can be algebraically obtained under the assumptions that the normal velocity and the background potential magnetic field in the Riemann fan are constant. The theoretical aspects of the HLLD approximate Riemann solver are focused on, in particular.

DOI： 10.1109/TPS.2010.2057451

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We performed a magnetohydrodynamic simulation of a formation process of coronal mass ejections (CMEs), focusing on the interaction (reconnection) between an ejecting flux rope and its ambient field. We examined three cases with different ambient fields: one had no ambient field, while the other two had dipole fields with opposite directions, parallel and anti-parallel to that of the flux rope surface. We found that while the flux rope disappears in the anti-parallel case, in the other cases the flux ropes can evolve to CMEs and show different amounts of flux rope rotation. The results imply that the interaction between an ejecting flux rope and its ambient field is an important process for determining CME formation and CME orientation, and also show that the amount and direction of the magnetic flux within the flux rope and the ambient field are key parameters for CME formation. The interaction (reconnection) plays a significant role in the rotation of the flux rope especially with a process similar to "tilting instability" in a spheromak-type experiment of laboratory plasma.

DOI： 10.1088/0004-637X/718/2/1305

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We performed a magnetohydrodynamic simulation of a formation process of coronal mass ejections (CMEs), focusing on the interaction (reconnection) between an ejecting flux rope and its ambient field. We examined three cases with different ambient fields: one had no ambient field, while the other two had dipole fields with opposite directions, parallel and anti-parallel to that of the flux rope surface. We found that while the flux rope disappears in the anti-parallel case, in the other cases the flux ropes can evolve to CMEs and show different amounts of flux rope rotation. The results imply that the interaction between an ejecting flux rope and its ambient field is an important process for determining CME formation and CME orientation, and also show that the amount and direction of the magnetic flux within the flux rope and the ambient field are key parameters for CME formation. The interaction (reconnection) plays a significant role in the rotation of the flux rope especially with a process similar to "tilting instability" in a spheromak-type experiment of laboratory plasma.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A 3-D magnetohydrodynamic (MHD) simulation is performed to reconstruct the interplanetary propagation of a coronal mass ejection (CME) that occurred on 13 December 2006. A spheromak-type magnetic field is superposed on a realistic ambient solar wind to reproduce the large-scale interplanetary magnetic field (IMF) associated with the CME. Here we show that a westward and southward directed spheromak CME with reasonable geometric, dynamic, and magnetic parameters reproduces the magnetic cloud, interplanetary shock, and sheath profiles as observed by in situ spacecraft. We suggest that the simple solar wind model developed in this study is topologically complex enough to be consistent with in situ observations, such as southward IMF associated with CMEs.

DOI： 10.1029/2009JA014167

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A 3-D magnetohydrodynamic (MHD) simulation is performed to reconstruct the interplanetary propagation of a coronal mass ejection (CME) that occurred on 13 December 2006. A spheromak-type magnetic field is superposed on a realistic ambient solar wind to reproduce the large-scale interplanetary magnetic field (IMF) associated with the CME. Here we show that a westward and southward directed spheromak CME with reasonable geometric, dynamic, and magnetic parameters reproduces the magnetic cloud, interplanetary shock, and sheath profiles as observed by in situ spacecraft. We suggest that the simple solar wind model developed in this study is topologically complex enough to be consistent with in situ observations, such as southward IMF associated with CMEs.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A novel, particle-based, probabilistic approach for the Simulation of cloud microphysics is proposed, which is named the super-droplet method (SDM). This method enables the accurate simulation of cloud microphysics with a less demanding cost in Computation. SDM is applied to a warm-cloud system, which incorporates sedimentation, condensation/evaporation and stochastic coalescence. The methodology to couple super-droplets and a non-hydrostatic model is also developed. It is confirmed that the result of our Monte Carlo scheme for the stochastic coalescence of super-droplets agrees fairly well with the solutions of the stochastic coalescence equation. The behaviour of the model is evaluated using a simple test problem, that of a shallow maritime cumulus formation initiated by a warm bubble. Possible extensions of SDM are briefly discussed. A theoretical analysis suggests that the Computational cost of SDM becomes lower than the spectral (bin) method when the number of attributes - the variables that identify the state of each super-droplet - becomes larger than some critical value, which we estimate to be in the range 2 similar to 4. Copyright (C) 2009 Royal Meteorological Society

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A novel, particle-based, probabilistic approach for the Simulation of cloud microphysics is proposed, which is named the super-droplet method (SDM). This method enables the accurate simulation of cloud microphysics with a less demanding cost in Computation. SDM is applied to a warm-cloud system, which incorporates sedimentation, condensation/evaporation and stochastic coalescence. The methodology to couple super-droplets and a non-hydrostatic model is also developed. It is confirmed that the result of our Monte Carlo scheme for the stochastic coalescence of super-droplets agrees fairly well with the solutions of the stochastic coalescence equation. The behaviour of the model is evaluated using a simple test problem, that of a shallow maritime cumulus formation initiated by a warm bubble. Possible extensions of SDM are briefly discussed. A theoretical analysis suggests that the Computational cost of SDM becomes lower than the spectral (bin) method when the number of attributes - the variables that identify the state of each super-droplet - becomes larger than some critical value, which we estimate to be in the range 2 similar to 4. Copyright (C) 2009 Royal Meteorological Society

DOI： 10.1002/qj.441

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPRINGER-VERLAG BERLIN  

A multiscale simulation method for gas detonations is proposed. This method is performed by the interlocking of a continuum fluid model and a particle based molecular model. The simulation system is spatially divided into the two kinds of domains, in one of which the near-thermal equilibrium is satisfied but not in the other. The dynamics of the near-thermal equilibrium domains is modeled by the continuum fluid dynamic equations. In the nonthermal equilibrium domain, which corresponds to the denotation front, the dynamics is modeled by the Boltzmann equation. This method has been tested on a model detonation system.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Agency for Marine-Earth Science and Technology  

地球シミュレータは, 2002年3月に稼働し7年の月日が経過した. この間, 機構内だけでなく, 国内外の多くの研究者に地球シミュレータは利用され, めざましい成果を挙げてきた. 地球シミュレータセンターは, 地球シミュレータ誕生と同時に設立され, 地球シミュレータセンター自身も新しいシミュレーション技術開発という形で, 大きな成果を挙げてきた. シミュレーションは, 科学的に未来を予測する唯一の手段であり, 学問としての科学だけでなく, 国民生活に貢献する技術という意味でも大きな役割を担っており,ここで開発された技術は, 人類の未来を設計する上で, 重要な意味を持っている.<br>地球シミュレータセンターでは, 平成16年度から始まった中期計画において, 3つのプログラム, 6つの研究グループが研究開発活動を行ってきた. すなわち,<br>・計算地球科学研究開発プログラム<br>大気・海洋シミュレーション研究グループ 固体地球シミュレーション研究グループ<br>・シミュレーション高度化研究開発プログラム<br>複雑性シミュレーション研究グループ 高度計算表現法研究グループ<br>・連結階層シミュレーション研究開発プログラム<br>アルゴリズム研究グループ 応用シミュレーション研究グループ<br>である.<br>以下に, これら6つの研究グループが創り出した研究成果を紹介する.

DOI： 10.5918/jamstecr.9.1_75

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

The reversal mechanism of a dipole magnetic field generated by dynamo action in a rotating spherical shell is investigated by a three-dimensional nonlinear magnetohydrodynamic simulation as well as a linear stability analysis. The emphasis of the study is on understanding the relationship between dipole reversal and the symmetry properties of the dynamo solution. As a result, first, it is found that there is a threshold of the magnetic Prandtl number, below which the dipole field is never reversed, and above which the reversal occurs at irregular intervals like the paleomagnetic evolution of the geodynamo. Second, it is shown that the dynamo process responsible for the generation of a dipole field (called "a-dynamo" in this paper) consists only of the antimirror symmetric magnetic field and the mirror symmetric velocity field with respect to the equatorial plane. Third, it is found that the components of the opposite symmetry to the a-dynamo grow only during the polarity reversal events and quickly decay afterwards. This indicates that the dipole field reversal and the loss of equatorial symmetry are tightly connected. In fact, it is clearly demonstrated by numerical analyses that the a-dynamo process is linearly unstable for the perturbation of opposite symmetry when the magnetic Prandtl number exceeds the threshold for dipole reversal. Mode coupling between the longitudinal Fourier components plays a crucial role in creating the instability. Based on the above results, it is proposed that symmetry-breaking instability could be the mechanism for dipole field reversal in the geodynamo process. The energy conversion between components of different symmetry is also analyzed in the quasistable polarity phase and in the polarity reversal phase, respectively. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2959120

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：UNIV CHICAGO PRESS  

DOI： 10.1086/588021

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Solar flares and coronal mass ejections are associated with rapid changes in field connectivity and are powered by the partial dissipation of electrical currents in the solar atmosphere. A critical unanswered question is whether the currents involved are induced by the motion of preexisting atmospheric magnetic flux subject to surface plasma flows or whether these currents are associated with the emergence of flux from within the solar convective zone. We address this problem by applying state-of-the-art nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA AR 10930 around the time of a powerful X3.4 flare. We compute 14 NLFFF models with four different codes and a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We discuss the relative merits of these models in a general critique of present abilities to model the coronal magnetic field based on surface vector field measurements. For our application in particular, we find a fair agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, ( 3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the similar to 10(32) erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The quantitative relationship between the magnetohydrodynamic ( MHD) activity of solar coronal arcade and the magnetic helicity injection, which is caused by shearing motion, has been investigated, using azimuthally symmetric model of MHD simulation. We have calculated several cases in which the width of the shearing region is varied and examined the relationship between the magnetic arcade dynamics and magnetic helicity evolution. As a result, it is found that as the shearing motion is imposed on narrower regions along each side of the magnetic inversion line, the magnetic arcade can be easily destabilized by the resistive tearing mode. However, in this case, even though reconnection driven by the tearing mode produces plasmoids, the plasmoid elevation is almost in proportion to the total amount of magnetic helicity contained in the arcade, and it is too slow to explain the trigger process of coronal mass ejections ( CMEs). On the other hand, in the case where the shearing motion is imposed on the entire region, much larger magnetic helicity injection is required to injected arcade in order to destabilize the system, compared to practical helicity injection measured in the solar corona. The results suggest that it may be difficult to trigger a CME just by the axisymmetric shearing motion and that some other mechanisms should be involved in the triggering process of a CME. The results also imply that the relation between the magnetic helicity and the overlying magnetic flux can be a key parameter for the CME occurrence.

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

The quantitative relationship between the magnetohydrodynamic ( MHD) activity of solar coronal arcade and the magnetic helicity injection, which is caused by shearing motion, has been investigated, using azimuthally symmetric model of MHD simulation. We have calculated several cases in which the width of the shearing region is varied and examined the relationship between the magnetic arcade dynamics and magnetic helicity evolution. As a result, it is found that as the shearing motion is imposed on narrower regions along each side of the magnetic inversion line, the magnetic arcade can be easily destabilized by the resistive tearing mode. However, in this case, even though reconnection driven by the tearing mode produces plasmoids, the plasmoid elevation is almost in proportion to the total amount of magnetic helicity contained in the arcade, and it is too slow to explain the trigger process of coronal mass ejections ( CMEs). On the other hand, in the case where the shearing motion is imposed on the entire region, much larger magnetic helicity injection is required to injected arcade in order to destabilize the system, compared to practical helicity injection measured in the solar c

DOI： 10.1029/2007JA012516

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Solar flares and coronal mass ejections are associated with rapid changes in field connectivity and are powered by the partial dissipation of electrical currents in the solar atmosphere. A critical unanswered question is whether the currents involved are induced by the motion of preexisting atmospheric magnetic flux subject to surface plasma flows or whether these currents are associated with the emergence of flux from within the solar convective zone. We address this problem by applying state-of-the-art nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA AR 10930 around the time of a powerful X3.4 flare. We compute 14 NLFFF models with four different codes and a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We discuss the relative merits of these models in a general critique of present abilities to model the coronal magnetic field based on surface vector field measurements. For our application in particular, we find a fair agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, ( 3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the similar to 10(32) erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection.

DOI： 10.1086/527413

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

We have developed a new interlocked simulation model to connect an Ion-Particle Hybrid simulation model (Hybrid) and an Energetic-Particle Hybrid simulation (EP-Hyb) model. In the conventional Ion-Particle Hybrid model, all ions are kinetically treated as particles. In the EP-Hyb model, non-thermal energetic ions are kinetically treated, and the thermal component is calculated as a fluid. The interlocked model is applied to an one-dimensional collision-less shock problem. The data of each hybrid model are exchanged through the boundary at every time-step. Resultantly, the present simulation can handle the full ion kinetics to investigate the injection problem at the shock transition region by the Hybrid model, and also the wave-particle interactions even in the far upstream region to investigate the diffusive acceleration process by the EP-Hyb model. Since the calculation cost of the EP-Hyb model is much smaller than that of the Hybrid model, with the interlocked simulation we can considerably reduce the computational demand.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

Robust and efficient approximate Riemann solvers for magnetohydrodynamics (MHD) are constructed. Particularly, a family of positively conservative Harten-Lax-van Leer (HLL)-type Riemann solvers, the so-called HLLD ('D' denotes Discontinuities), HLLR ('R' denotes Rotational), HLLC ('C' denotes Contact), and HLL solvers, is systematically considered.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

Active region NOAA 10930 produced the first X-class flare observed by the Hinode satellite. Fortunately, the data covers the time span before and after the X-class flare arising on December 13, 2006 in this active region. During this event, the Hinode satellite clearly observed the typical features of a flare: two ribbon and post flare loop structures seen by SOT, sigmoidal structure before the onset, and subsequent cusp loop structure seen by XRT. We analyzed the three-dimensional magnetic structure of the region before and after the flare on Dec.13, 2006 using the Non-Linear Force-Free (NLFF) extrapolation method based on extended magnetofrictional method.
As a result of the NLFF extrapolation, we found that, before the flare onset, strong sheared structures were formed on the neutral line. Furthermore, we revealed that a sigmoidal structure was not formed of a single loop, but was composed of strong multiple sheared field. On other the hand, after the flare, elongated magnetic flux is partially formed and a part of magnetic shear was released. The result indicates that the part; of NLFF relaxes toward the potential like field in this event.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Recently, several methods that measure the velocity of magnetized plasma from time series of photospheric vector magnetograms have been developed. Velocity fields derived using such techniques can be used both to determine the fluxes of magnetic energy and helicity into the corona, which have important consequences for understanding solar flares, coronal mass ejections, and the solar dynamo, and to drive time-dependent numerical models of coronal magnetic fields. To date, these methods have not been rigorously tested against realistic, simulated data sets, in which the magnetic field evolution and velocities are known. Here we present the results of such tests using several velocity-inversion techniques applied to synthetic magnetogram data sets, generated from anelastic MHD simulations of the upper convection zone with the ANMHD code, in which the velocity field is fully known. Broadly speaking, the MEF, DAVE, FLCT, IM, and ILCT algorithms performed comparably in many categories. While DAVE estimated the magnitude and direction of velocities slightly more accurately than the other methods, MEF's estimates of the fluxes of magnetic energy and helicity were far more accurate than any other method's. Overall, therefore, the MEF algorithm performed best in tests using the ANMHD data set. We note that ANMHD data simulate fully relaxed convection in a high-beta plasma, and therefore do not realistically model photospheric evolution.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Many kinds of simulation models have been developed to understand the complex plasma systems. However, these simulation models have been separately performed because the fundamental assumption of each model is different and restricts the physical processes in each spatial and temporal scales. On the other hand, it is well known that the interactions among the multiple scales may play crucial roles in the plasma phenomena (e.g. magnetic reconnection. collisionless shock), where the kinetic processes in the micro-scale may interact with the global structure in the fluid dynamics. To take self-consistently into account such multi-scale phenomena, we have developed a new simulation model by directly interlocking the fluid simulation of the magnetohyrdodynamics (MHD) model and the kinetic simulation of the particle-in-cell (PIC) model. The PIC domain is embedded in a small part of MHD domain. The both simulations are performed simultaneously in each domain and the bounded data are frequently exchanged each other to keep the consistency between the models. We have applied our new interlocked simulation to Alfven wave propagation problem as a benchmark test and confirmed that the waves can propagate smoothly through the boundaries of each domain. (C) 2007 Elsevier Inc. All rights reserved.

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Many kinds of simulation models have been developed to understand the complex plasma systems. However, these simulation models have been separately performed because the fundamental assumption of each model is different and restricts the physical processes in each spatial and temporal scales. On the other hand, it is well known that the interactions among the multiple scales may play crucial roles in the plasma phenomena (e.g. magnetic reconnection. collisionless shock), where the kinetic processes in the micro-scale may interact with the global structure in the fluid dynamics. To take self-consistently into account such multi-scale phenomena, we have developed a new simulation model by directly interlocking the fluid simulation of the magnetohyrdodynamics (MHD) model and the kinetic simulation of the particle-in-cell (PIC) model. The PIC domain is embedded in a small part of MHD domain. The both simulations are performed simultaneously in each domain and the bounded data are frequently exchanged each other to keep the consistency between the models. We have applied our new interlocked simulation to Alfven wave propagation problem as a benchmark test and confirmed that the waves can propagate smoothly through the boundaries of each domain. (C) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcp.2007.09.011

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Recently, several methods that measure the velocity of magnetized plasma from time series of photospheric vector magnetograms have been developed. Velocity fields derived using such techniques can be used both to determine the fluxes of magnetic energy and helicity into the corona, which have important consequences for understanding solar flares, coronal mass ejections, and the solar dynamo, and to drive time-dependent numerical models of coronal magnetic fields. To date, these methods have not been rigorously tested against realistic, simulated data sets, in which the magnetic field evolution and velocities are known. Here we present the results of such tests using several velocity-inversion techniques applied to synthetic magnetogram data sets, generated from anelastic MHD simulations of the upper convection zone with the ANMHD code, in which the velocity field is fully known. Broadly speaking, the MEF, DAVE, FLCT, IM, and ILCT algorithms performed comparably in many categories. While DAVE estimated the magnitude and direction of velocities slightly more accurately than the other methods, MEF's estimates of the fluxes of magnetic energy and helicity were far more accurate than any other method's. Overall, therefore, the MEF algorithm performed best in tests using the ANMHD data set. We note that ANMHD data simulate fully relaxed convection in a high-beta plasma, and therefore do not realistically model photospheric evolution.

DOI： 10.1086/522422

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

In this study, we investigated magnetic helicity injection rates among active regions of various sizes. We analyzed 78 active regions (more than 600 magnetograms), using the vector magnetograms obtained with the Solar Flare Telescope of NAOJ and SoHO/MDI magnetograms. We used a method proposed by Kusano et al. (2002, 2004) to evaluate the helicity injection. Magnetic fluxes of analyzed regions are from 2 x 10(12) Wb to 4 x 10(14) Wb. Unsigned magnetic helicity injection rates are from 10(19) Wb(2) s(-1) to 10(23) Wb(2) S-1. From a scatter plot of the magnetic flux and the unsigned magnetic helicity injection rate, we found that the magnetic helicity injection rate has an upper limit for a given value of the magnetic flux, and this upper limit is inversely proportional to the magnetic flux. We discuss these results with a model of the helicity injection due to helical turbulence (E-Effect, Longcope, Fisher, & Pevtsov 1998).

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPRINGER-VERLAG BERLIN  

A new methodology for the, simulation of multiscale processes, called Macro-Micro Interlocked (MMI) Simulation, is introduced. The MMI simulation is carried out by the two-way connection of different numerical models, which may handle macroscopic and microscopic dynamics, respectively. The MMI simulation are applied to several multiscale phenomena, for instance, cloud formation, gas detonation, and plasma dynamics. The results indicate that the MMI simulation provide us an effective and prospective framework for multiscale simulation.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

We numerically investigated the three-dimensional (3D) stability and the nonlinear dynamics of flux tube embedded in magnetic arcade. As a results, we found that the flux tube is unstable to the kink mode instability, as the system approach to the loss-of-equilibrium state. The 3D simulation shows that when the flux tube is long enough, it can escape from arcade with almost constant speed after the accelerated launching due to the kink instability. In the case of the short flux tube, however, the flux tube ascending is failed at some height. The strong current sheet is formed in the lower part of the long flux tube at late phase as a consequence of the instability, whereas the current sheet can not be maintained in the case of short flux tube. Therefore, the formation of the current sheet at late phase may have some relation to the ejective eruption of the flux tube.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

Some important observations have shown that the strong correlation between emerging flux and eruptions of quiescent filaments (Feynman & Martin, 1995; Wang & Sheeley, 1999). Chen & Shibata (2000) performed two-dimensional simulations including a flux rope in the corona, and their results suggest that the eruption process is triggered by the emerging flux through the reconnection. Our purpose in this paper is to investigate that '' how a filament is produced and how an eruption process can be initiated by the emerging flux and what effects of three-dimensionality appear in the process of eruption ''. For that purpose, we performed three-dimensional numerical simulations of the emerging flux model. nom our results, a filamentary structure is produced from the coronal arcade field by the reconnection process, and when the reconnection process proceeds effectively, the produced structure is ejected by the magnetic force. These processes can thought to be a new mechanism of the eruption which is different from, for example, the one in Fan & Gibson (2004).

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

The formation mechanism of sigmoidal structure in the solar corona and the transition process from long-lived sigmoid to flare eruption are studied on the basis of the Taylor's minimum energy principle and the three-dimensional magnetohydrodynamic numerical simulations. The simulation results indicate that magnetic reconnection driven by the resistive tearing mode instability growing on current sheet, where magnetic shear is steeply reversed, may cause the formation of sigmoidal structure. The mechanism of that can be explained as the spontaneous manifestation of the Taylor's minimum energy state in magnetic arcade geometry. Furthermore, it is also numerically demonstrated that the formation of sigmoid can be followed by the eruption of magnetic flux. In the eruption, however, the sigmoidal flux itself is not ejected upward, but it is collapsed by the reconnection with overlaying magnetic field. The results are consistent with the reversed shear flare model recently proposed by Kusano et al., which predicts that the coronal eruption is triggered by the collapsing of magnetic arcade due to the annihilation of positive and negative magnetic helicity.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

The compute power required in the simulation of mutually cooperating systems in the physical sciences is huge. Therefore, it is common to simulate one system and treat others as parameters or environmental conditions to the simulated system. Macro-Micro Interlocked (MMI) simulation framework has been proposed to simulate such cooperating systems. In this paper, we study the feasibility of applying this framework on the simulation of macro-micro economic model. This simulation allows us to observe the system's behaviour at the macro and micro levels concurrently. Policy changes at the macroeconomic level may affect the behaviour of the entities at the microeconomic level. Similarly, the behaviour changes at the microeconomic level may effect the macroeconomic system. We implement an MMI simulation library suitable for execution on a cluster of PCs. At this early stage, the experiment shows a promising result which provides us with a foundation to experiment with a larger model. © 2007 IEEE.

DOI： 10.1109/PADS.2007.22

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Three-dimensional magnetohydrodynamics of the Solar coronal plasma is investigated by numerical simulation, aiming to understand the mechanisms of the Solar flare onset. It is demonstrated by the simulations that the resistive tearing mode instability growing on the magnetic shear inversion layer can drive the large-scale eruption through the mutual excitation of double reconnections. It is also revealed that the instability is able to cause the magnetohydrodynamic energy relaxation, in which the typical sigmoidal structure is self-organized prior to the onset of eruption. The Simulation results predict that both the formation of sigmoids and the onset of flares should occur around the electric current sheet where the magnetic shear is steeply reversed. It is consistent with the reversed-shear flare model and the vector magnetograph observations.

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CAMBRIDGE UNIV PRESS  

A new simulation model is developed, in which the interaction between the macroscopic and microscopic plasma processes is able to be taken into account self-consistently. Magnetohydrodynamic (MHD) simulation and particle-in-cell (PIC) simulation are directly connected and performed simultaneously. This MHD-PIC connection model is first applied to the study of the quiet auroral are formation process. It is an example of our challenge to create the holistic simulation framework, that is, the heterogeneous schemes that can be unified by the state-of-the-art numerical technique. In this paper, we will explain the algorithm of our new model and show the results which have been calculated on the Earth Simulator.

DOI： 10.1017/S0022377806005356

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CAMBRIDGE UNIV PRESS  

Three-dimensional magnetohydrodynamics of the Solar coronal plasma is investigated by numerical simulation, aiming to understand the mechanisms of the Solar flare onset. It is demonstrated by the simulations that the resistive tearing mode instability growing on the magnetic shear inversion layer can drive the large-scale eruption through the mutual excitation of double reconnections. It is also revealed that the instability is able to cause the magnetohydrodynamic energy relaxation, in which the typical sigmoidal structure is self-organized prior to the onset of eruption. The Simulation results predict that both the formation of sigmoids and the onset of flares should occur around the electric current sheet where the magnetic shear is steeply reversed. It is consistent with the reversed-shear flare model and the vector magnetograph observations.

DOI： 10.1017/S0022377806005423

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CAMBRIDGE UNIV PRESS  

The CAVE-type virtual reality (VR) system was introduced for scientific visualization of large-scale data in the plasma simulation community about a decade ago. Since then, we have been developing a VR visualization software. VFIVE, for general CAVE systems. Recently, we have integrated an open-source visualization library, the Visualization Toolkit (VTK), into VFIVE. Various visualization methods of TTK can be incorporated and used interactively in VFIVE.

DOI： 10.1017/S0022377806005253

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The three-dimensional stability and the nonlinear dynamics of a flux rope embedded in a magnetic arcade are investigated using magnetohydrodynamic (MHD) simulations, with the goal of understanding the mechanism of filament eruption in the solar corona. The flux rope equilibrium proposed by Forbes in 1990 is adopted as the initial state of the three-dimensional simulation, and we find that the equilibrium is linearly unstable to the kink mode instability, when the system approaches the loss-of-equilibrium state. The three-dimensional simulation demonstrates that when the flux rope is long enough, it can escape from the arcade at an almost constant speed after the accelerated launching phase due to the kink instability. The continuous ascending of the flux rope is driven by the nonlinear growth of several kink modes. In the case of a short flux rope, however, the flux rope ascension fails at some height. This suggests that the flux rope eruption must proceed through the multiple stages, which are driven by the loss of stability in the launching phase and by the loss of equilibrium in the late ascending phase. Since the short rope could not come up to the critical height for the transition from the first to the second stage, the ascending must stop. The role of magnetic reconnection in the late ascending phase and the formation mechanism of density cavity, which corresponds to dimming region observed in CMEs, is also discussed using the simulation results.

DOI： 10.1086/503153

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Two-dimensional, nonlinear magnetohydrodynamic simulations in a compressible plasma to investigate magnetic energy release during the process of forced magnetic reconnection are carried out. This is in order to study the heating of the Sun's corona where it is believed that reconnection is induced by the photospheric motions. A sheared force-free field is perturbed by a transitory slow disturbance (pulse) at the boundary. This disturbance triggers the formation of a current sheet that subsequently releases stored magnetic energy through magnetic reconnection. Previously, it has been shown that for small boundary perturbations, the simulation results are consistent with the previous analytic theory based on a linear approach. For larger amplitude perturbations, or close to the threshold for tearing instability, the evolution shows nonlinear behavior. Solar coronal heating may arise due to a series of reconnection events, and a primary aim of this work is to study the interaction of such heating events. Thus, the perturbations are applied at the boundary by successive pulses. It is found that following the second driving pulse, the current sheet expands along the separatrix before relaxing to a reconnective equilibrium with magnetic islands and releasing even more magnetic energy for the same amplitude perturbation. Here, the previous work is extended to study long wavelength perturbations for which the system exhibits even stronger nonlinear aspects. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2200630

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The formation mechanism of sigmoidal structure in the solar coronal magnetic field is studied using the three-dimensional magnetohydrodynamic numerical simulations, based on the so-called reversed-shear flare model recently proposed by Kusano et al. The simulation results clearly indicate that magnetic reconnection driven by the resistive tearing mode instability growing on the magnetic shear inversion layer can cause the spontaneous formation of sigmoidal structure. Furthermore, it is also numerically demonstrated that the formation of the sigmoids can be followed by the explosive energy liberation, if the sigmoids contain sufficient magnetic flux. This implies that the reversed-shear flare model can provide a self-consistent explanation for the formation of sigmoids as well as for the onset of eruption, which is driven by magnetic reconnection above sigmoids. The geometric relationship between the sigmoidal structure and the minimum energy state predicted by J. B. Taylor in 1974 is examined. The result suggests that the sigmoidal formation could be understood as a manifestation of the minimum energy state, which has the excess magnetic helicity compared to the bifurcation criterion of the linear force-free field. The consistency with the observations of magnetic helicity is also discussed.

DOI： 10.1086/432570

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

A new multi-state Harten-Lax-van Leer (HLL) approximate Riemann solver for the ideal magnetohydrodynamic (MHD) equations is developed based on the assumption that the normal velocity is constant over the Riemann fan. This assumption is same as that used in the HLLC ("C" denotes Contact) approximate Riemann solver for the Euler equations. From the assumption, it is naturally derived that the Riemann fan should consist of four intermediate states for Bx ≠ 0, whereas the number of the intermediate states is reduced to two when Bx = 0. Since the intermediate states satisfied with all jump conditions in this approximate Riemann system are analytically obtained, the multi-state HLL Riemann solver can be constructed straightforwardly. It is shown that this solver can exactly resolve isolated discontinuities formed in the MHD system, and hence named as HLLD Riemann solver. (Here, "D" stands for Discontinuities.) It is also analytically proved that the HLLD Riemann solver is positively conservative like the HLLC Riemann solver. Indeed, the HLLD Riemann solver corresponds to the HLLC Riemann solver when the magnetic field vanishes. Numerical tests demonstrate that the HLLD Riemann solver is more robust and efficient than the linearized Riemann solver, and its resolution is equally good. It indicates that the HLLD solver must be useful in practical applications for the ideal MHD equations. © 2005 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcp.2005.02.017

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We studied the relationship between magnetic helicity injection and the formation of sigmoidal loops. We analyzed seven active regions: three regions showed coronal loops similar to the potential field, and four regions showed the sigmoidal loops. The magnetic helicity injection rate was evaluated using the method proposed by Kusano et al. In order to compare the helicity of regions of various sizes, we defined the normalized helicity injection rate as the magnetic helicity injection rate divided by the magnetic flux squared. We found that the sigmoidal regions and nonsigmoidal regions have comparable normalized helicity injection rates. Next, we calculated the magnetic helicity content of the sigmoidal loops by using the magnetic flux tube model (Longcope & Welsch) and compared it with the magnetic helicity injected from around the footpoints of three sigmoidal loops. For two sigmoidal loops, it is found that these values are comparable. Another loop showed significant disagreement between helicity injection rate and its magnetic helicity content. Excluding this region on the basis of its complexity ( perhaps multiple loops forming a sigmoidal loop), we can conclude that geometric twist of the sigmoidal loops is consistent with the magnetic helicity injected from around the footpoints of the sigmoidal loops.

DOI： 10.1086/429363

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The correlation between magnetic helicity injection across the photosphere and soft X-ray activity in the solar corona is statistically investigated for seven active regions appearing in the years 1997 - 2000. The magnetic helicity flux into the solar corona is analyzed by the induction equation method, using magnetograms observed by the Michelson Doppler Imager on SOHO and by the vector magnetograph at the National Astronomical Observatory of Japan. Soft X-ray activity is evaluated from the data observed by the Yohkoh soft X-ray telescope (SXT). Soft X-ray activity of active regions in nonflare phases is found to correlate better with unsigned magnetic helicity flux than with the simple integration of the magnetic helicity flow. In addition, several magnetic variables, e. g., magnetic flux and electric current flux, are investigated, and it is confirmed that any fluxes given by the area integration of magnetic variables are well correlated with soft X-ray activity. However, for themagnetic helicity flow, not only the whole area flux but also the local intensity correlates well with the soft X-ray intensity. The relation between the spatial structure of the magnetic shear and soft X-ray activity is also investigated, and it is revealed that structural complexity in the magnetic shear tends to increase the efficiency of energy liberation in the solar corona. These results indicate that the magnetic helicity injected from the photosphere is relevant to the heating process in the solar corona, although several magnetic variables, not only magnetic helicity, could be related to that.

DOI： 10.1086/426806

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Magnetic reconnection is a strong candidate for a coronal heating mechanism, and heating by forced magnetic reconnection is investigated here. Two dimensional, nonlinear magnetohydrodynamic simulations are used to investigate forced magnetic reconnection in a compressible plasma. The reconnection occurs when a sheared force-free field is perturbed by a slow disturbance (pulse) at the boundary which is representative of the solar corona where the reconnection is induced by the photospheric motions. The case of driving by successive pulses, which generate a series of heating events which may interact with each other, is considered. This is in order to model the heating of the corona by a series of nanoflare events. For small perturbations, the simulation results are consistent with the previous analytic theory based on linear approach where a current sheet is formed initially at the resonant surface followed by reconnection and then release of magnetic energy. For large amplitude perturbations, or close to the threshold for tearing instability, the system exhibits strong nonlinear aspects. Following the second driving pulse, the current sheet expands along the separatrix before relaxing to a reconnective equilibrium and releasing even more magnetic energy for the same amplitude perturbation. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.1831278

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

Generation and annihilation processes of magnetic helicity in solar coronal active regions are investigated based on the observations and the simulations. We first examined the reliability of the numerical techniques, which enable to measure the magnetic helicity flux through the photosphere based on the magnetogram data. Secondly, in terms of the new technique, we found that magnetic helicities of the both signs are simultaneously injected into active regions. Motivated by this result, finally, we investigated the nonlinear process of the magnetic helicity annihilation, using the three-dimensional numerical simulations. The simulations clearly indicated that the helicity reversal can cause the eruption of large-scale plasmoid through the nonlinear process of the resistive instability growing on the helicity inversion layer. From these studies, we point out that the annihilation of magnetic helicity is a key process for the onset mechanism of solar flares.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：CAMBRIDGE UNIV PRESS  

DOI： 10.1017/S1743921305000669

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the possibility that magnetic reconnection between oppositely sheared magnetic loops works as a trigger mechanism of solar flares, based on three-dimensional numerical simulations. The simulations were carried out by applying a slow footpoint motion, which reverses a preloaded magnetic shear, in the vicinity of the magnetic neutral line. The simulation results clearly indicated that the reversal of magnetic shear can cause a large-scale eruption of the magnetic arcade through a series of two different kinds of magnetic reconnections. The first reconnection is initiated by the resistive-tearing mode instability growing on the magnetic shear inversion layer and annihilates the sheared magnetic fluxes, which are oppositely directed along the magnetic neutral line. As a result of this, the magnetic arcade collapses into the reconnection point, and a new current sheet is generated above and below the shear inversion layer. The generation of new current sheets is followed by another magnetic reconnection, which drives the eruption of the sheared magnetic arcade. Mutual excitation of the two reconnections may explain the explosive property of the flare onset.

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：UNIV CHICAGO PRESS  

We have investigated the possibility that magnetic reconnection between oppositely sheared magnetic loops works as a trigger mechanism of solar flares, based on three-dimensional numerical simulations. The simulations were carried out by applying a slow footpoint motion, which reverses a preloaded magnetic shear, in the vicinity of the magnetic neutral line. The simulation results clearly indicated that the reversal of magnetic shear can cause a large-scale eruption of the magnetic arcade through a series of two different kinds of magnetic reconnections. The first reconnection is initiated by the resistive-tearing mode instability growing on the magnetic shear inversion layer and annihilates the sheared magnetic fluxes, which are oppositely directed along the magnetic neutral line. As a result of this, the magnetic arcade collapses into the reconnection point, and a new current sheet is generated above and below the shear inversion layer. The generation of new current sheets is followed by another magnetic reconnection, which drives the eruption of the sheared magnetic arcade. Mutual excitation of the two reconnections may explain the explosive property of the flare onset.

DOI： 10.1086/421547

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PHYSICAL SOC JAPAN  

Three dimensional local simulation was performed to investigate the energy conversion and the dynamo action in the magnetohydrodynamic (MHD) turbulence due to the magnetorotational instability (MRI) in a differentially rotating disk, using Arbitrary Lagrangian Eulerian method. As a result, it was found that the turbulence plays a role to convert the magnetic energy to the kinetic energy, if the shear parameter q defined by -dln Ω/dln R is less than 2.3, where Ω and R are the angular velocity and the disk radius, respectively. It means that amplification of the magnetic energy in the MRI is mainly due to the twisting effect of differential rotation rather than a result of the turbulent dynamo action. When q ≥ 2.5, the energy conversion rate from the kinetic energy to the magnetic energy is switched to positive, because low modes, which are destabilized by the Rayleigh instability, can work for the turbulent dynamo. On the other hand, it is also revealed that, the α-dynamo effect exists at least for q ≥ 0.75, although the contribution to the amplification of the magnetic energy is very small. From these results, it can be concluded that, even though the MRI is able to amplify the magnetic energy, the turbulence due to the MRI is less effective as a driver of the conventional dynamo process, unless the Rayleigh instability arises. ©2004 The Physical Society of Japan.

DOI： 10.1143/JPSJ.73.94

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

We analyzed the magnetic helicity injection in NOAA Active Region 8011 with the method proposed by Kusano et al. (2002). It was found that the helical geometry of a sigmoidal loop in this region is consistent with the magnetic helicity injected from the foot points of the loop. We also made a statistical study of the correlation between X-ray intensity and magnetic helicity injection. We found that the sum of the absolute values of the magnetic helicity injection shows good correlation with the X-ray luminosity. The estimated flux of magnetic free energy injection is not highly correlated with the X-ray flux, because the former quantity is overestimated in our simple method.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

Several new methodologies to detect the magnetic helicity injection activity across the photosphere into the solar corona have been developed recently. We briefly review the basic principle of the typical two methods, the so-called local correlation tracking (LCT) method and the induction equation (IE) method. The reliability of them is examined using a three-dimensional model field. The benchmark examination indicates that, if the vector magnetic field data are available, the IE method can greatly improve the accuracy of the helicity flux measurement. The physical implication of the recent results of the magnetic helicity measurement is also discussed. In particular, we emphasize the possibility that not only the intensity but also the complexity of the magnetic helicity injection from the photosphere could activate the energy liberation process in the solar corona.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/jspf.79.496

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

On the basis of the three-dimensional numerical simulation, we study the effect of density stratification on the thermal convection in a rotating spherical shell. Three different density-stratified equilibria, which have different polytropic indices, are adopted as the initial state of the simulation. The density ratio between the bottom and the top of the domain is in the range from 2.0 to 10.7, and the Taylor number is fixed to 104. It is found that when the Rayleigh number is slightly above the instability threshold, the convection structure is hardly affected by the difference of stratification, whereas when the Rayleigh number is much larger than the instability threshold, the nonlinear solution in the strongly stratified equilibria bifurcates into the sectorial convection and the quasi-axisymmetric zonal convection. Through the bifurcation from the sectorial solution to the quasi-axisymmetric solution, the sign of the averaged kinetic helicity is changed in each hemisphere (negative to positive in the northern hemisphere). The results suggest that the solar and the stellar convections must be sensitive to the density stratification.

DOI： 10.1086/344138

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We develop a new methodology that can determine magnetic helicity flux as well as Poynting flux across the photosphere based on magnetograph observation. By applying this method, we study the injection mechanism of magnetic helicity and magnetic free energy into the solar corona. In order to derive the helicity and energy fluxes, first the velocity tangential to the solar surface is constructed by applying a correlation tracking technique on the magnetic observation, and second, the velocity component normal to the photosphere is derived from the condition that the magnetic evolution must be consistent with the induction equation. Through this procedure, we can determine the helicity and energy fluxes separately for the shear motion effect and for the flux emergence effect. Based on this new method, NOAA Active Region 8100 was analyzed from 1997 November 1 to 5 using data observed by the Solar and Heliospheric Observatory Michelson Doppler Interferometer and the vector magnetograph at the National Astronomical Observatory of Japan (NAOJ) in Tokyo. The results indicate that the photospheric shear motion and the flux emergence process have equally contributed to the helicity injection and have supplied magnetic helicity of opposite signs into this active region.

DOI： 10.1086/342171

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

We develop a new methodology that can determine magnetic helicity flux as well as Poynting flux across the photosphere based on magnetograph observation. By applying this method, we study the injection mechanism of magnetic helicity and magnetic free energy into the solar corona. In order to derive the helicity and energy fluxes, first the velocity tangential to the solar surface is constructed by applying a correlation tracking technique on the magnetic observation, and second, the velocity component normal to the photosphere is derived from the condition that the magnetic evolution must be consistent with the induction equation. Through this procedure, we can determine the helicity and energy fluxes separately for the shear motion effect and for the flux emergence effect. Based on this new method, NOAA Active Region 8100 was analyzed from 1997 November 1 to 5 using data observed by the Solar and Heliospheric Observatory Michelson Doppler Interferometer and the vector magnetograph at the National Astronomical Observatory of Japan (NAOJ) in Tokyo. The results indicate that the photospheric shear motion and the flux emergence process have equally contributed to the helicity injection and have supplied magnetic helicity of opposite signs into this active region.

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

Three-dimensional magnetohydrodynamic (MHD) instability in the solar coronal magnetic arcades, which are subject to the constant shearing motion at the feet, was investigated based on the numerical simulations. It was found that the magnetic arcade instability for three-dimensional modes undulating the magnetic arcade can grow if the aspect ratio (defined as the ratio of the arcade length to the width) is larger than unity. In particular, when the aspect ratio is much larger than unity, the nonlinear coupling among several modes dominates the dynamics. As a result, in a very long magnetic arcade, three-dimensional reconnection, which takes place in a limited region in the magnetic arcade, may proceed continuously.

DOI： 10.1086/339910

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

We developed a new methodology to measure magnetic helicity as well as magnetic energy injection into the solar corona from magnetograph observations, and we studied the relationship between helicity injection and X-ray activity in the solar corona. In order to calculate the gauge-invariant helicity flux and the Poynting flux across the photosphere, first the velocity tangential to the photospheric surface is constructed by applying the correlation tracking technique on SOHO/MDI observations, and second the normal velocity is calculated by solving the induction equation as an inverse-problem using data from SOHO/MDI and the Solar Flare Telescope at NAOJ in Tokyo. The helicity injection as well as the free energy build-up is analyzed for active region NOAA 8100 from November 1 to 4, 1997. The results indicate that the emerging flux and the shear flow inject magnetic helicity of opposite sign (positive and negative, respectively) into the active region prior to a series of flares. Furthermore it is found that during the helicity injection process magnetic free energy in the amount of 5 x 1032 erg was supplied, which is much more than the X-ray flux emitted by the flares.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two-dimensional numerical simulations are used to investigate nonlinear aspects of forced magnetic reconnection in a zero β highly conducting plasma. This is representative of the solar corona, where reconnection may be induced by external perturbations, e.g., at the photospheric boundary of the corona. The aim is to investigate the energy dissipation by the reconnection, which may provide a mechanism for heating the coronal plasma. The field is taken to he initially a sheared force-free equilibrium in a slab, and the effects of applying a slow deformation to the boundaries are investigated. Previous analytical studies assuming small departures from the initial equilibrium have found that a current sheet forms during an initial ideal phase of evolution, which subsequently relaxes to a reconnected equilibrium, releasing some magnetic energy. The linear theory predicts that the energy release has a singularity when the field is marginally stable to the tearing mode. The nonlinear evolution of the field is calculated numerically, focusing on the energy release. In particular, the strongly nonlinear behavior is studied in the parameter regime in which the linear theory breaks down. It is found that nonlinearities become strong close to the marginal stability point, and for such highly sheared fields, the energy released by reconnection is large even for weak boundary deformations. © 2001 American Institute of Physics.

DOI： 10.1063/1.1329151

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

The density stratification effects on the thermal convection in a rotating spherical shell, which is the representative of the solar convection zone, are investigated by three dimensional numerical simulations. It is found that, the convection structure in the strongly stratified system is switched from parallel cells aligned to the rotation axis to zonal rolles dominated by the longitudinally averaged mode, as the Rayleigh number increases much larger than the stability threshold. Corresponding to this structural transition, the averaged kinetic helicity reverses the sign in each hemisphere (from negative to positive in the northern hemisphere). The results indicate that the density stratification is much important for the nonlinear convection process in the rotating spherical shell.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：TERRA SCIENTIFIC PUBL CO  

A three-dimensional reconnection process, which is caused by the magnetic arcade instability, is investigated using numerical simulations. It is found that the aspect ratio (defined as the ratio of the length to the width of the magnetic arcade) is a crucial parameter to control the nonlinear dynamics. When the aspect ratio is rather small, the dynamics is governed by a symmetric mode, and more explosive reconnection happens. In a longer arcade, on the other hand, an undulating three-dimensional activity arises. It suggests that the variety in solar coronal activity may be caused by the differece in arcade shape.

DOI： 10.1186/BF03353260

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPRINGER  

Web of Science

記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：Blackwell Publishing Ltd  

Solar coronal magnetic field plays a role as a channel through which the magnetic helicity is transported from the sun into the interplanetary space. If the coronal field forms the arcades, and if the magnetic Reynolds number is sufficiently large, the helicity transportation proceeds intermittently, even in the case that the helicity is constantly supplied from the sun. The intermittent transportation is a cyclic process which consists of the helicity storage, magnetic reconnection, and the plasmoid ejection. It is a result of the competition between the destabilization by the photospheric activity and the spontaneous stabilization caused by the magnetic arcade instability. The total helicity is well conserved even in the energy relaxation process, so that Taylor’s hypothesis on the selective dissipation is applicable also to the solar corona. However, the numerical simulations indicate that the energy relaxation is even partial, and that the free energy cannot be exhausted, because the photospheric boundary gives a stronger constraint than Taylor’s theory predicted. The coronal field could evolve around the marginally stable limit, which locates in the intermediate region between the stable and the unstable linear force free solutions. The results suggest that, even if there is no external trigger, the coronal plasma is able to generate intermittent activities like flares.

DOI： 10.1029/GM111p0149

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPRINGER  

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AMER INST PHYSICS  

The propagation of electro-static waves in a-fluid dusty plasma system is investigated. We study the dynamics of the dust particles and ions in the a-fluid dusty plasma system. We find that the electro-static waves in dusty plasma are developed as the new modes. When we assume that the charge-up process in the equilibrium can be eliminated, these modes approach to Ion-Acoustic mode (Q(d0) = 0) Or Dust-ion-Acoustic mode (P-d0 = 0).

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Institute of Physics Inc.  

Nonlinear dynamics of magnetic buoyancy instabilities for the Parker-type and interchange-type modes are numerically investigated with the aim of understanding the emerging mechanism of solar coronal magnetic loops. Two-dimensional nonlinear magnetohydrodynamic (MHD) simulations of the magnetic buoyancy instabilities are performed in a highly stratified domain consisting of two temperature regions corresponding to the corona and the chromosphere, respectively. First, it is revealed that the angle between the wave vector and the magnetic field at the top interface of the magnetic layer is a crucial parameter controlling the basic properties of the instability. Second, it is found that the magnetic buoyancy instability in the sheared field grows nonlinearly larger than in the shearless field, although the magnetic shear reduces the linear growth rate. This is due to the Parker-type mode being destabilized by the nonlinear effect of the interchange-type instabilities. Third, it is shown that the magnetic buoyancy instability can drive magnetic reconnections which create isolated flux regions. © 1998 American Institute of Physics.

DOI： 10.1063/1.872944

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

Three-dimensional global magnetohydrodynamic (MHD) simulations are performed in order to investigate the global structure and the dynamics of the Jovian magnetosphere. Particularly, we investigate the influence of the planetary rotation onto the magnetospheric structure. The effects of the interplanetary magnetic field (IMF) in the solar wind are also considered. The simulation results clearly indicate that the dawn-dusk asymmetries are generated due to the effect of the planetary rotation. The plasmoid can be also observed in the tail region. The neutral lines of the magnetic field, however, appear obliquely from the dawn-dusk line, so that the location of the plasmoid is quite different from that in the Earth's magnetosphere.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

The theoretical proposition, that solar hares are self-organization processes to realize the Taylor's minimum energy state [K.Kusano, ct al., Astrophys. J., 441 942 (1995)], is examined by the numerical simulations. The simulation shows that the self-organization process indeed takes place, and that a rapid energy relaxation process is achieved through magnetic reconnection on thin current sheets, as expected from the theory. However, it is also clarified that, since the line-tied condition on the photosphere severely restricts the energy relaxation in addition to Taylor's hypothesis on total helicity conservation. Furthermore, we consider the storage mechanism of the free energy to drive solar flares, and find that a substantial free energy can be stored in the coronal magnetic field through a competitive process between the helicity injection due to the photospheric motion and the instability in the coronal arcade system.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

Magnetic reconnection, which arises from the nonlinearity of the magnetohydrodynamic instability in the solar coronal loops, is analyzed in detail by the numerical simulations. It is revealed that the time-scale of the current sheet formation does not depend on the linear growth rate of the initial instability, and it is scaled by the Alfven transit times. It is also found that! when the magnetic Reynolds number is in the range from 10(3) to 10(4), the length of the current layer in the reconnection site is geometrically limited to the scale of the loop feet interval and is hardly affected by the change in the resistivity. Consequently, the width of the current layer is proportional to the square root of the resistivity.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

We perform the tyro-dimensional magnetohydrodynamic (MHD) simulation which can calculate either the generation and the evolution of the solar coronal magnetic loops with a magnetic shear. The linear stability analysis reveals that, if the magnetic field has a stronger shear, higher-wavenumber perturbations are destabilized because of the excitation of the interchange mode, so that the unstable region in the wavenumber space is enlarged. In the nonlinear simulation, it is observed that as the result of the initial perturbation growing, the magnetic flux emerges into the corona and the coronal loop is generated, It is also observed that when the perturbation of the short-wavelength is imposed to the strongly sheared magnetic held. the isolated flux tube is generated through the magnetic reconnection process.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

We study the relaxation phenomena of the reversed field pinch (RFP) plasma with a radio-frequency (rf) current drive. We develop the magnetohydrodynamic code, in which the effect of the rf current drive is included in the induction equation as an external electric field obtained from the ray tracing of the fast magnetosonic wave. As the results of simulations, we observe that the rf current drive can effectively reduce the disturbance due to the kink mode instabilities and it may sustain the reversed held without the MHD relaxation dynamics, These results suggest that the rf current drive is a prospective method to enable a quiet sustainment of the RFP configuration.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

The magnetohydrodynamic (MHD) relaxation process in the solar coronal magnetic field is investigated in terms of three-dimensional numerical simulations. We consider the dynamics of magnetic loops, which is caused by the photospheric twisting motion. It is found that, as a result of the rising of the magnetic loops, isolated flux tubes (plasmoids) are generated on top of the loops through the magnetic reconnection process. It is revealed that the plasmoid formation can be explained as a transition between two different solutions of the Woltjer-Taylor minimum energy state. (Kusano, Suzuki, & Nishikawa 1995). Furthermore, the three-dimensional effect in the transition dynamics is investigated in detail by the Fourier mode analysis.

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：JAPAN SOCIETY PLASMA SCIENCE &NUCLEAR FUSION RESEARCH  

The three-dimensional (3D) compressible magnetoconvection in a rectangular domain with a horizontal magnetic field is investigated using the numerical simulation. The 3D calculations are carried out adopting the result from the two-dimensional convection simulations as the initial condition. It is observed that the stable roll convection in the 2D system is unstable in the 3D system, and a complex spatial-temporal structure is generated.

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Institute of Physics Inc.  

Effects of electron-positron pair creation on the stationary one-dimensional propagation of relativistically coupled electromagnetic and electrostatic waves are studied based on the self-consistent model presented in the previous paper for an electron-ion plasma [L. N. Tsintsadze and K. Nishikawa, Phys. Plasmas 3, 511 (1996)]. The pair-created particles are treated as a cold electron-positron plasma at their creation point. In addition to the results similar to those obtained for the electron-ion plasma, a new type of instability of the finite amplitude plane wave is found which is purely growing in the wave frame near threshold. A novel solution describing an envelope shock which represents a wake-field excitation by a solitary electromagnetic pulse is obtained by taking into account the trapping of the pair-created particles in the upstream region. © 1997 American Institute of Physics.

DOI： 10.1063/1.872207

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union  

The nonlinear interaction of a rapidly rotating magnetosphere with the external supersonic plasma flow is investigated by using the three-dimensional global magneto-hydrodynamic (MHD) simulation. The results of the simulations clearly indicate that various dawn-dusk asymmetries are generated due to the effect of the rotation. Particularly, the location of the plasmoid, which is generated in the tail region of the rotating magnetosphere, is quite different from the case without rotation. It is also found that distinctive magnetospheric structures such as the plasma disc are largely modified in response to the dynamic pressure in the external plasma flow. Copyright 1997 by the American Geophysical Union.

DOI： 10.1029/97GL52739

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Yukawa Institute for Theoretical Physics  

INSAM (Institute for Numerical Simulations and Applied Mathematics) in Hiroshima University is a group consists of researchers whose major are Numerical Simulations and/or Applied Mathematics. It covers wide range of science: mathematics, physics, chemistry, biology and earth &amp
planetary system. In this report the current activities of INSAM are presented. The performance of Intel Paragon, which is a main computer resource of INSAM, and its implementation for our applications will be also discussed.

DOI： 10.1143/PTPS.122.51

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：KLUWER ACADEMIC PUBL  

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：KLUWER ACADEMIC PUBL  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

The general solution of the Woltjer-Taylor minimum energy state is found in the solar coronal geometry, which is modeled as a rectangular domain. It is shown that the solution bifurcates into two different states when the magnetic helicity integral or the geometrical factor defined as the ratio of the height to the width of the domain is satisfactorily increased. Based on this analysis, it is theoretically proposed that a solar flare is a transition process between two different Woltjer-Taylor states, which are generated as a result of the bifurcation. The theory predicts that a solar flare is triggered when the vertical size of the coronal magnetic loop becomes longer than the horizontal size. The topological structure in the coronal magnetic field must be dramatically changed in the transition process. The result implies that in general, magnetic reconnection must be accompanied by a solar flare. The numerical simulation shows that the transition process is dynamically realized as a result of a twisting motion on the photosphere. Based on this theory, disagreements among recent simulation works on the plasmoid formation problem can be consistently explained.

DOI： 10.1086/175413

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

The general solution of the Woltjer-Taylor minimum energy state is found in the solar coronal geometry, which is modeled as a rectangular domain. It is shown that the solution bifurcates into two different states when the magnetic helicity integral or the geometrical factor defined as the ratio of the height to the width of the domain is satisfactorily increased. Based on this analysis, it is theoretically proposed that a solar flare is a transition process between two different Woltjer-Taylor states, which are generated as a result of the bifurcation. The theory predicts that a solar flare is triggered when the vertical size of the coronal magnetic loop becomes longer than the horizontal size. The topological structure in the coronal magnetic field must be dramatically changed in the transition process. The result implies that in general, magnetic reconnection must be accompanied by a solar flare. The numerical simulation shows that the transition process is dynamically realized as a result of a twisting motion on the photosphere. Based on this theory, disagreements among recent simulation works on the plasmoid formation problem can be consistently explained.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The energy conversion process as well as the plasma heating mechanism in the starting-up phase of driven reconnection is investigated in detail using two-dimensional magnetohydrodynamic (MHD) simulation. It is revealed that the compressional heating effect is predominant in this phase rather than the Ohmic and the viscous heating. The predominance of the compressional heating means that the plasma flow energy is considerably converted to the thermal energy. The strong compression takes place in the process during which the fast shock is generated in the downstream region of the reconnection point. The plasma heating due to nonsteady reconnection is briefly discussed as a promising mechanism for the anomalous ion heating, which is observed in reversed-field pinch (RFP) experiments. © 1993 American Institute of Physics.

DOI： 10.1063/1.860521

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Whether it is induced by an ideal (current driven) instability or by an external force, plasma flow causes a change in the magnetic field configuration and often gives rise to a current intensification locally, thereby a fast driven reconnection being driven there. Many dramatic phenomena in magnetically confined plasmas such as magnetospheric substorms, solar flares, magnetohydrodynamic (MHD) self-organization, and tokamak sawtooth crash, may be attributed to this fast driven reconnection. Using a fourth-order MHD simulation code it is confirmed that compressibility of the plasma plays a crucial role in leading to a fast (MHD time scale) driven reconnection. This indicates that the incompressible representation is not always applicable to the study of a global dynamical behavior of a magnetically confined plasma. © 1992 American Institute of Physics.

DOI： 10.1063/1.860295

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：The Japan Society of Plasma Science and Nuclear Fusion Research  

The computer simulation has played an important role for the research of reversed-field pinch (REP) physics. Especially, in order to elucidate essential nonlinear mechanisms, the simulation study is a much useful methodology. It is described how the computer simulation has been applied to solve the self-reversal and the self-sustainment processes.

DOI： 10.1585/jspf1958.65.528

CiNii Books

その他リンク： https://jlc.jst.go.jp/DN/JALC/00009529311?from=CiNii

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The toroidal phase locking process of kink modes in a reversed field pinch (RFP) plasma is investigated in detail by means of magnetohydrodynamic (MHD) simulation. The physical mechanism of phase locking is clarified. The two most dominant linearly unstable kink modes govern the evolution of other kink modes, whereby phase locking takes place. It is confirmed that the phase locking process is not a special phenomenon of plasmas with a resistive boundary, but a common feature of the MHD relaxation process in RFPs. The relation between the phase locking process and the MHD relaxation process is briefly discussed. It is found that phase locking is reproduced cyclically in the sustainment process. © 1991, IOP publishing Ltd.

DOI： 10.1088/0029-5515/31/10/010

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Progress of Theoretical Physics  

Recent progress in super-computers has opened a new tool for the study of nonlinear dynamics in plasmas. This paper reviews the recent computer simulation studies for the self-organization and self-relaxation processes in MHD plasmas carried out by the Hiroshima group. Taylor's conjecture for the selective dissipation of magnetic energy keeping the total magnetic helicity canstant is confirmed and the mechanisms for formation and maintenance of the reversed field pinch configuration are explained in terms of the self-relaxation of the plasma due to a driven magnetic reconnection triggered by ideal MHD helical kink unstable modes and their nonlinear couplings.

DOI： 10.1143/PTPS.99.206

CiNii Books

その他リンク： http://dl.ndl.go.jp/info:ndljp/pid/10883515

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c39890001208

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Based on theoretical and computational considerations, it is confirmed that magnetic reconnection driven nonlinearly by a kink instability plays a key role in the magnetohydrodynamic relaxation. An important finding is that the relaxation takes the form of either global relaxation (e.g., the reversed field pinch relaxation) or local relaxation (e.g., the tokamak sawtooth relaxation), depending on whether the driven reconnection is total (antiparallel) or partial (partially antiparallel). © 1988 American Institute of Physics.

DOI： 10.1063/1.859100

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The sixth order wave equation which results from a finite temperature expansion of the Vlasov equation is solved globally in the ion cyclotron range of frequencies. A perpendicularly stratified, onedimensional slab plasma is assumed. The diamagnetic drift and the associated anisotropy are included in the unperturbed distribution function to ensure a self-adjoint system. All x-dependence in the plasma pressure and magnetic field is retained along with the electric field parallel to B. Thus, Landau damping of the ion Bernstein wave is included self-consistently. Because of the global nature of the solution, the evanescent short wavelength Bernstein waves do not grow exponentially as in shooting methods. Strong variations occur in the absorption and in the structure of the wave fields as resonance topology is varied. Solutions to the complete sixth order differential equation are compared to those from an approximate second order equation based on local dispersion theory. © 1988 IOP Publishing Ltd.

DOI： 10.1088/0029-5515/28/1/007

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.866085

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The characteristics of a toroidal discharge with qa ≈ 1/2 is studied on TORIUT-6. Ultra low q equilibria that are stable against the global kink mode are realized through MHD relaxation and are shown to be characterized by dq/dr &lt
0 and a hollow current profile. The stable state lasts for 600 μs, which is of the order of the classical diffusion time. These experimental observations are consistent with non-linear MHD simulation results. © IOP Publishing Ltd.

DOI： 10.1088/0029-5515/27/7/010

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We propose a theory that a new type of magnetic reconnection, nonlinear driven reconnection, is triggered during the nonlinear development of an m=1 helical kink-mode instability. This reconnection process can well explain nonlinear reconnection observed in the previous simulation and can be a candidate for the self-reversal mechanism in the reversed-field pinch. © 1985 The American Physical Society.

DOI： 10.1103/PhysRevLett.54.808

Scopus

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：英語

記述言語：日本語

総ページ数：178p   記述言語：日本語

CiNii Books

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語

記述言語：日本語   出版者・発行元：プラズマ・核融合学会  

太陽黒点活動にはSchwabeサイクルと呼ばれる約11年の周期変動と様々な長期変動があることがわかっている.特に,17世紀のマウンダー極小期に代表される大極小期は地球気候にも少なくない影響を与えたことが示唆されている.しかし,太陽黒点の周期活動と長期変動のメカニズムは未だに十分理解されていない.太陽表面の振動から太陽内部の状態を再現する日震学の進展とコンピュータによる数値モデルの発達により,太陽活動の基本的な性質を説明すると共にこれを予測する試みが進みつつある.

CiNii Books

その他リンク： http://dl.ndl.go.jp/info:ndljp/pid/10459106

記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）  

記述言語：日本語   出版者・発行元：北海道大学低温科学研究所 = Institute of Low Temperature Science, Hokkaido University  

洋上の浅い層積雲にエアロゾルと雲の相互作用が及ぼす影響を, 持続的にエアロゾルが形成される理想化された気象システムの数値計算により調べる. 雲微物理過程の数値計算には超水滴法を使い, エアロゾル・雲粒・降水粒子のふるまいを統一的に計算する.大気流体場は準圧縮近似の下で音波モードとそれ以外を分割して数値計算する. 初期のエアロゾル数密度によらず系は数日後にある定常状態に落ち着くこと, その定常状態はエアロゾル生成率が大きくなるに伴い積雲から層雲に転移することを見る. 今回のモデルでは, 気相や液相での化学反応までは考慮していないためエアロゾルと雲の相互作用が完全に表現できてはおらず, また数値計算も鉛直２次元で行うため, この結果はあくまで予備的なものである.The influence of aerosol-cloud interactions on the behavior of marine stratocumulus is investigated through numerical simulations of an idealized meteorological system in which aerosols are formed continuously. The super-droplet method is used for the simulation of cloud microphysical processes, with which the time evolution of aerosol/cloud/precipitation particles is calculated in a unified manner. For the simulation of atmospheric fluid dynamical processes, the quasi-compressible approximation and the sound mode splitting method are applied. The system gradually evolves to reach its final steady state in a few days, which is irrelevant to the initial number density of aerosols. A transition of the final steady state from cumuli to strati occurs when the aerosol formation rate is increased. Because the chemical reaction in the gas phase and the liquid phase is not incorporated, the model is not detailed enough to describe aerosol-cloud interactions. Further, the numerical simulations are performed in two dimensions. For these reasons, the results obtained are still all preliminary

CiNii Books

その他リンク： http://hdl.handle.net/2115/55063

記述言語：日本語   出版者・発行元：プラズマ・核融合学会  

CiNii Books

記述言語：日本語   出版者・発行元：プラズマ・核融合学会  

CiNii Books

記述言語：英語   出版者・発行元：Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：岩波書店  

CiNii Books

記述言語：日本語   出版者・発行元：日本天文学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

CiNii Books

その他リンク： https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=376745

記述言語：日本語   出版者・発行元：プラズマ・核融合学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

J-GLOBAL

記述言語：日本語  

CiNii Books

記述言語：日本語   出版者・発行元：日本計算工学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本計算工学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

Toward peta-scale computing era, a next-generation MHD solver that is accurate and robust enough for any parameter regimes from almost incompressible turbulences to hypersonic flows should be developed. One of the key techniques for the next-generation solver must be a divergence cleaning method for the magnetic filed, which primarily affects the robustness of the multidimensional MHD solver particularly in high-resolution simulations. In this paper, several divergence cleaning methods including new methods are comparatively studied based on the HLLD Riemann solver.

CiNii Books

記述言語：日本語   掲載種別：研究発表ペーパー・要旨（全国大会，その他学術会議）   出版者・発行元：日本学術会議 「機械工学委員会・土木工学・建築学委員会合同IUTAM分科会」  

磁気圏－電離層結合系で生じるマクロ不安定性を計算する電磁流体コードと、磁気圏から電離層へ流入する電子によるミクロ不安定性を計算する粒子コードを連結したシミュレーションモデルにより、静穏時オーロラアーク形成の物理過程について調べた。その結果、フィードバック不安定性[1]により、アーク構造が形成される様子が観測された。さらに、粒子モデル計算で得られた加速電子のエネルギースペクトルから、大気分子励起による発光強度を算出し、オーロラアーク発光までいたる物理過程の再現をおこなった。
[1] T. Sato, J. Geophys. Res., 83, 1042, 1978.

DOI： 10.11345/japannctam.57.0.214.0

記述言語：日本語   出版者・発行元：National Committee for IUTAM  

太陽活動は地球環境に様々な影響を及ぼす。例えば、太陽系最大の爆発である太陽フレアとコロナ質量放出（CME）は地球近傍の電磁環境を乱すことが知られており、こうした宇宙天気現象の予測技術の開発は衛星システムの維持管理などの視点から求められている。一方、太陽黒点活動が地球の平均気温に影響していることは古くから指摘されており、宇宙と地球環境の関係（宇宙気候）の理解は地球環境の予測のためにも重要な課題である。本研究では、宇宙天気・宇宙気候現象における複雑な物理過程を複数の数値モデルの連結でとらえる連結階層シミュレーション研究の試みについて、その現状と展望を議論する。

DOI： 10.11345/japannctam.57.0.216.0

記述言語：日本語   出版者・発行元：日本流体力学会  

We have recently developed a new interlocked MHD model of the Sun-Earth system, in order to understand the relationship between solar and geomagnetic storms, and to predict space weather phenomena. In this paper, we introduce the entire design of the new model, and show the preliminary results of numerical experiments for early phase of a solar storm.

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

We have recently developed a new interlocked MHD modeling of the Sun-Earth system to understand the relationship between solar and geomagnetic storms, and to predict the associated space weather phenomena. In this study, we report our modeling results of the global solar wind structures including the propagation of a coronal mass ejection.

CiNii Books

記述言語：日本語   出版者・発行元：日本地質学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

J-GLOBAL

記述言語：日本語   出版者・発行元：日本気象学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

A carbuncle-free multi-state Harten-Lax-van Leer (HLL)-type approximate Riemann solver for HD and MHD is newly proposed. From phenomenological consideration for numerical shock instabilities like a carbuncle phenomenon, we guess that the instabilities may appear when a numerical viscosity is insufficient for a shear wave rather than for a contact wave. In this study, the numerical viscosity for the tangential momentum is selectively added assuming the single-state tangential velocity in the Riemann fan. The new solver can be effectively embedded into the higher HLLC and HLLD Riemann solver using the usual shock-fix algorithm.

CiNii Books

記述言語：日本語   出版者・発行元：The Visualization Society of Japan  

Cloud formations and precipitation are highly-complicated phenomena, and the accurate modeling of them is a crucial subject for meteorological simulations. Recently, we developed a new algorithm, which enables the first-principle simulation of cloud formation process, by introducing a new numerical concept called "super-droplet".<BR>In this paper, we report about the visualization of the cloud formation-precipitation simulation using the super-droplet method. The technique to visualize the distribution of all droplets included in a cumulus cloud will be explained, and some application results of it will be also presented for the analysis of droplet size spectrum, cloud motion, and the optical property of cloud, respectively.

DOI： 10.3154/jvs.26.Supplement2_27

J-GLOBAL

記述言語：日本語   出版者・発行元：可視化情報学会  

DOI： 10.3154/jvs.26.Supplement1_87

CiNii Books

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

We develop a novel cloud microphysics model, called Super Droplet Model (SDM), which enables accurate calculation for the motion, growth by condensation and evaporation, and coalescence of all the droplets in a cloud with reasonable cost in computation. We couple SDM and a non-hydrostatic cloud dynamics model and demonstrate a regional simulation of cloud formation and precipitation.

CiNii Books

記述言語：日本語   出版者・発行元：日本気象学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

We developed a new three-dimensional Magnetohydrodynamic (MHD) code for global simulation of coronal mass ejections in the solar corona. In this code, ideal MHD equations with gravity are solved by finite volume method with the monotonic upstream schemes for conservation laws (MUSCL) which achieves 3rd order spatial resolution, the HLLD nonlinear approximate Riemann solver, and the 2nd order Runge-Kutta time integration. An initial condition is built up with magneto-hydrostatic equilibrium of source surface potential field.

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

A fluid description of plasmas is useful to investigate the global structure in space plasma, such as the magnetosphere and heliosphere. It can reproduce the time evolution of macroscopic variations of density, bulk velocity and pressure. On the other hand, the microscopic dynamics of plasmas should be described by spatial and velocity distribution in the phase space. Wave-particle interaction process is the typical example for the application of the microscopic description. For these micro- and macroscopic description, different kinds of numerical approach may work well, respectively, e.g. MHD simulation for the macroscopic phenomena and PIC simulation for microscopic process. However, it is widely accepted that the cross-scale interaction between micro and macro processes plays a crucial role, for instance, in the diffusion region in the magnetic reconnection process. Therefore, a new model which can treat MHD-scale dynamics including particle kinetic effects is necessary. We have developed the new simulation method called "Interlocked simulation", in which MHD and PIC simulations are simultaneously performed. Here, we show its algorithm and some examples.

CiNii Books

記述言語：日本語   出版者・発行元：日本天文学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：日本流体力学会  

We performed three-dimensional numerical simulations of the emergence of magnetic flux from the convectiove zone into the corona and its reconnection with a preexisting ambient coronal arcade field. Initially the flux tube in the convective zone is perturbed and becomes unstable to the Parker instability. The instability causes the rise and the expansion of the flux tube into the corona and the field comes into contact with the arcade field. When the upcoming field and the coronal arcade field generate current sheets between them, the reconnection occurs, causing profound changes in their connectivity. The local heating and the high-speed outflows caused by the reconnection can be seen in our simulations. We investigate how the changes in the angle of the arcade relative to the magnetic neutral line, lead to the different physical processes.

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：英語   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

The analysis of the magnetic helicity injection into active region NOAA 8100 is shown. This region is known as a source of many coronal activities such as flares. It is found that most of the flare events occurred about half a day after the helicity injection rate changed its sign. And the positions of Ha emission in flares well correspond to the helicity inversion lines in space. These results suggest that the sign-reversal of the helicity injection rate is a key signature of flare activities. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(03)00773-7

Web of Science

記述言語：日本語   出版者・発行元：The Japan Society of Plasma Science and Nuclear Fusion Research  

Although magnetic reconnection is believed to be a key process in solar flares, the flares' triggering mechanism remains a long-standing problem. In order to resolve this issue, the physical linkage between the magnetohydrodynamic (MHD) process in the macroscopic scale and the plasma kinetics in the microscopic scale has to be understood. Multiple-scale simulation, which can precisely describe the nonlinear process of the MHD equations as well as the complexity in the solar corona, will play a crucial role in this field of study.

DOI： 10.1585/jspf.79.496

CiNii Books

その他リンク： https://jlc.jst.go.jp/DN/JALC/00229591198?from=CiNii

記述言語：英語   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

We developed a new methodology which can determine magnetic helicity flux across the photosphere based on the magnetograph observation. In order to derive the helicity flux, first the velocity tangential to the solar surface is constructed by applying a correlation tracking technique on the magnetic observation, and secondly the velocity component across the photosphere is derived from the condition that the magnetic evolution must be consistent with the induction equation. Through this procedure, we can determine the helicity flow across the photosphere as a function of time and space. Based on this new method, we analyzed magnetic helicity of the active regions NOAA 906 and 9077, using the data taken by SOHO/MDI and the vector magnetograph at NAOJ/Tokyo. As a result, it was revealed that positive and negative helicity is supplied in each region simultaneously. In particular, temporary activation of the helicity injection of the both signs was observed prior to X-class flare events in the GOES classification. The investigation on the helicity distribution suggests some relationship between flare onset and the increase of complexity in the helicity structure. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(03)00772-5

Web of Science

記述言語：英語   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

Although magnetic reconnection is believed to be a key process for solar flares, the onset mechanism of flares remains as a long-standing problem. In this paper, we propose a new model for solar flares, in which magnetic reconnection converts oppositely-sheared field into the shear-free field. This process can be understood as the annihilation of magnetic helicities with, different signs, and it is consistent with the recent results of the helicity observations. Numerical simulations were carried, which show that, if the helicity is sharply, reversed within a magnetic arcade, reconnection quickly grows in the helicity inversion layer, driving explosive dynamics. The explosive process appears as a result of nonlinear instability, which grows faster than exponentially with time. Based on the results, we predict that the coexistence of the positive and negative helicity is crucial for the onset of flares. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(03)00765-8

Web of Science

記述言語：日本語   出版者・発行元：プラズマ・核融合学会  

Magnetohydrodynamics (MHD) provide a very important model for our understanding of the structure and evolution of space and astronomical plasmas, such as the Sun, solar corona, and planetary magnetosphere. This paper outlines two key concepts, reconnection and dynamo, those play an essential role in the energetic activity of a variety of astronomical and space plasmas.

CiNii Books

その他リンク： http://dl.ndl.go.jp/info:ndljp/pid/10454465

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

太陽観測衛星「ようこう」によって, 太陽フレアがプラズマ閉じ込め実験におけるエネルギー解放過程と同様に, 磁気再結合(磁気リコネクション)を通して発生することが観測的に初めてつきとめられた. 一方, 電磁流体力学的最小エネルギー原理に基づいた解の分岐理論によって, 太陽フレアの発生機構を実験室プラズマと共通する枠組の中で理解することができるようになった. 太陽フレアは, 局所的なエネルギー散逸を通して引き起こされる高温プラズマ中のエネルギー遷移過程である. 天文学的興味のみならず, 高温プラズマの一般的性質を知る手掛かりとして太陽フレアは再認識されつつある.

DOI： 10.11316/butsuri1946.53.656

CiNii Books

その他リンク： https://jlc.jst.go.jp/DN/JALC/00056151794?from=CiNii

記述言語：英語   出版者・発行元：KOREAN PHYSICAL SOC  

The nonlinear magnetohydrodynamics (MHD) in solar flares is considered using two dimensional numerical simulations. The results are analyzed based on the bifurcation theory of the linear force-free field [K. Kusano, et al., Astrophys. J. 441 942 (1995)]. The simulation results show that a transition from a loop type configuration into an island type configuration indeed takes place as the bifurcation theory predicted. The dependence of the transition dynamics on the resistivity is considered in detail.

Web of Science

記述言語：英語   出版者・発行元：KOREAN PHYSICAL SOC  

The nonlinear magnetohydrodynamics (MHD) in solar flares is considered using two dimensional numerical simulations. The results are analyzed based on the bifurcation theory of the linear force-free field [K. Kusano, et al., Astrophys. J. 441 942 (1995)]. The simulation results show that a transition from a loop type configuration into an island type configuration indeed takes place as the bifurcation theory predicted. The dependence of the transition dynamics on the resistivity is considered in detail.

Web of Science

記述言語：日本語  

CiNii Books

記述言語：日本語  

CiNii Books

記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

Three-dimensional dynamics of solar coronal magnetic loops, which is caused by the photospheric twisting motion, is investigated in detail by using magnetohydrodynamic numerical simulations. It is found that, as a result of the rising of the magnetic loops, isolated flux tubes (plasmoids) are generated on top of the loops through magnetic reconnection. During the reconnection process, the magnetic energy of the mode coupled with the potential held is partially converted into the mode decoupled from it. We also analyze the linear stability of the coupled mode and reveal that it is destabilized when the loop height and the magnetic helicity exceed the critical values predicted from the bifurcation theory. Furthermore, we reveal that three-dimensional mode couplings have the effect of concentrating the helicity into an unstable mode, as well as the effect of reducing the growth rate of the instability.

Web of Science

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：英語   出版者・発行元：UNIV CHICAGO PRESS  

The bifurcation structure as well as the stability property of the solar coronal magnetic arcades in a linear force-free field (LFFF) is carefully investigated. It is clarified that two different modes can cause the bifurcation of the minimum energy arcade profile: the symmetric mode (SM), which has a zero wavevector, and the undulating mode (UM), which has a nonzero wavevector parallel to the magnetic neutral lines. Depending on the geometry and the magnetic helicity contained in the arcades, the minimum energy state is switched among three different solutions of the LFFF: the coupled solution (CS), which consists only of the components coupled with the potential held; the mixed solution (MS), which is composed of the CS and the SM; and the MS of the CS and the UM. It is found that, once the LFFF bifurcates into the CS and the MS, the CS is always unstable against the SM or the UM. Based on the discussion about the relationship between the excess energy and the growth rate, it is proposed that the preflare state is a nonlinearly growing stage of these instabilities rather than a metastable state.

Web of Science

記述言語：英語   出版者・発行元：PHYSICAL SOC JAPAN  

One-dimensional transport equations for pulsed-laser induced space-charge distributions in GaAs crystals have been computed using a finite difference procedure by two models; (a) Model A for i-GaAs with an applied dc electric field under a uniform illumination over the crystal and (b) Model B for n- and i-GaAs without the electric field under a half illumination to simulate the ''transient thermoelectric effect'' (TTE). With Model A, the temporal and spatial evolutions of restored space-charge density of photoexcited electrons and holes are obtained, from which an induced electric field is found to oscillate with a single frequency of plasma oscillations (0.3-2THz), in satisfactory agreement with reported experiments. Model B calculations have revealed that near the boundary between the illuminated and non-illuminated regions, the appreciable enhancement of space-charge densities and induced electric fields are observed, which diffuse or drift toward a positive x direction, showing characteristic damping oscillations with two frequency components f(0) due to the doped donor electrons and f(1) due to the doped and photoexcited electrons of plasma oscillations. Furthermore, the induced TTE voltages measured across both ends of the crystal without dc electric field are simulated to show similar coherent plasma oscillations.

DOI： 10.1143/JPSJ.65.803

Web of Science

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：英語   掲載種別：速報，短報，研究ノート等（学術雑誌）   出版者・発行元：INT ATOMIC ENERGY AGENCY  

Double tearing modes in ultra-low-q equilibria have been simulated by three-dimensional MHD calculations. Spatially localized MHD relaxation is shown to be driven by double tearing modes, which bring the field configuration in the unstable region to a Taylor-like relaxed state. When the pitch minimum of the initial state is located near the centre of the plasma, the central value of q decreases rapidly and the outer magnetic island replaces the original magnetic axis. When the pitch minimum is located near the wall, the central core region remains stable and reconnection occurs in a limited intermediate region.

DOI： 10.1088/0029-5515/31/1/017

Web of Science

記述言語：英語   出版者・発行元：INT ATOMIC ENERGY AGENCY  

DOI： 10.1088/0029-5515/30/10/009

Web of Science

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：英語   出版者・発行元：核融合科学研究所  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：英語   出版者・発行元：PHYSICAL SOCIETY JAPAN  

DOI： 10.1143/JPSJ.56.963

Web of Science

DOI： 10.1063/1.866085

DOI： 10.1063/1.866085

記述言語：英語  

By means of 3D magnetohydrodynamic simulations, the relaxation process in the finite β reversed-field pinch (RFP) is investigated. It is confirmed that the nonlinear reconnection process is the dominant mechanism of the RFP relaxation even in the system of finite β. The nonlinear reconnection rate is almost halved compared with that in the zero β case. The relaxed state of finite β is dynamically achieved. This state has a flat pressure profile and is well approximated by the Bessel-function model in the central region. The simulation result agrees with the partially relaxed state model. The β-limit is estimated based on the Suydam criterion, and consequently, it is found that the stable area on the F-θ diagram is narrowed as the heat loss decreases. © 1987, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.56.963

Scopus

記述言語：英語   掲載種別：書評論文，書評，文献紹介等  

The relaxation process in the reversed field pinch has been studied extensively with three-dimensional magnetohydrodynamic simulations. It is found that the non-linear coupling between multiple helicity modes plays a leading role in the relaxation process. Specifically, the (m
n)=(0
1) island is excited as a result of non-linear coupling between the linearly unstable m=l modes, with a toroidal mode number difference of one. The m=0 island is then subject to axisymmetric non-linear reconnection whereby reversed flux is effectively generated in the outer region. It should be noted that although the axisymmetric non-linear reconnection of m=0 island is the dominant relaxation process, helical non-linear reconnection of linearly unstable m=l modes also plays some role in the relaxation of the whole system. It is also found that through this multiple helicity relaxation process, Taylor's minimum energy state is realized. The simulation results are generally consistent with experimental observations in the sustainment phase. This indicates that the multiple helicity relaxation process is of fundamental importance in the maintenance of the reversed field during the sustainment phase as well as in the self-reversal during the set-up phase. The relation between relaxation and aspect ratio has also been examined and it is found that the relaxation process is not strongly affected by the aspect ratio. © IOP Publishing Ltd.

DOI： 10.1088/0029-5515/27/5/011

Scopus

記述言語：英語   出版者・発行元：INT ATOMIC ENERGY AGENCY  

DOI： 10.1088/0029-5515/26/8/005

Web of Science

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books