Updated on 2023/10/25

写真a

 
IWAI Kazumasa
 
Organization
Institute for Space-Earth Environmental Research Division for Heliospheric Research Associate professor
Graduate School
Graduate School of Science
Title
Associate professor
Contact information
メールアドレス
Profile
名古屋大学 宇宙地球環境研究所 太陽圏研究部 准教授。福井県武生市出身。2012年、東北大学大学院理学研究科博士後期課程終了。博士(理学)。国立天文台野辺山太陽電波観測所、情報通信研究機構、米国国立電波天文台を経て2017年4月より現職。専門は、太陽圏物理学、電波天文学。特に電波観測を用いた太陽圏の観測的研究や宇宙天気予報に関する研究をしている。また次世代電波望遠鏡の開発研究も推進している。
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Degree 1

  1. 博士(理学) ( 2012.3   東北大学 ) 

Research Interests 8

  1. Solar Wind, Sun, Space Weather, Space, Radio telescope, Digital devices

  2. Space Weather

  3. Solar Wind

  4. Sun

  5. Data assimilation

  6. Digital devices

  7. Space

  8. Radio telescope

Research Areas 3

  1. Natural Science / Space and planetary sciences

  2. Natural Science / Astronomy

  3. Social Infrastructure (Civil Engineering, Architecture, Disaster Prevention) / Disaster prevention engineering

Research History 4

  1. Nagoya University, Institute for Space-Earth Environmental Research   Division for Heliospheric Research   Associate professor

    2017.4

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    Country:Japan

  2. National Radio Astronomy Observatory   Guest Researcher

    2017.1 - 2017.3

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    Country:Japan

  3. National Institute of Information and Communications Technology (NICT)   Applied Electromagnetic Research Institute   JSPS research fellow

    2015.4 - 2017.3

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    Country:Japan

  4. National Astronomical Observatory of Japan   Nobeyama Solar Radio Observatory   Researcher

    2012.4 - 2015.3

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    Country:Japan

Education 2

  1. Tohoku University   Graduate School, Division of Natural Science

    2007.4 - 2012.3

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    Country: Japan

  2. Tohoku University   Faculty of Science

    2003.4 - 2007.3

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    Country: Japan

Professional Memberships 4

  1. The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)

  2. International Astronomical Union (IAU)

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  3. The Astronomical Society of Japan

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  4. JAPAN GEOSCIENCE UNION

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Committee Memberships 4

  1. apan Solar Physics Community (JSPC)   Steering Committee  

    2021.12   

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    Committee type:Other

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  2. 文部科学省 科学技術・学術政策研究所 科学技術予測センター   専門調査員  

    2020.4   

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    Committee type:Government

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  3. 日本天文学会   天文月報編集委員  

    2019.6 - 2023.5   

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    Committee type:Academic society

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  4. 国立天文台 研究交流委員会   研究交流委員  

    2018.7 - 2022.6   

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Awards 4

  1. Obayashi Early Career Scientist Award

    2020.11   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   Studies on solar atmosphere and heliosphere based on the development of leading-edge radio telescopes

    Kazumasa Iwai

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  2. Sensyuu-kai Early Career Scientist Award

    2020.10   Alumni Association, Tohoku University Department of Physics  

    Kazumasa Iwai

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  3. Student Presentation Award (Aurora Medal)

    2012.5   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   Fine spectrum structures of solar radio type-I burst

    Kazumasa Iwai

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  4. Student Presentation Award (Aurora Medal)

    2009.5   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   The development of wide band solar radio polarization spectrograph

    Kazumasa Iwai

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Papers 41

  1. Forecasting Heliospheric CME Solar-Wind Parameters Using the UCSD Time-Dependent Tomography and ISEE Interplanetary Scintillation Data: The 10 March 2022 CME Reviewed

    Bernard V. Jackson, Munetoshi Tokumaru, Kazumasa Iwai, Matthew T. Bracamontes, Andrew Buffington, Ken’ichi Fujiki, Go Murakami, Daniel Heyner, Beatriz Sanchez-Cano, Mathias Rojo, Sae Aizawa, Nicolas Andre, Alain Barthe, Emmanuel Penou, Andrei Fedorov, Jean-Andre Sauvaud, Shoichiro Yokota, Yoshifumi Saito

    Solar Physics   Vol. 298 ( 5 )   2023.5

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    Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    Abstract

    Remotely sensed interplanetary scintillation (IPS) data from the Institute for Space-Earth Environmental Research (ISEE), Japan, allows a determination of solar-wind parameters throughout the inner heliosphere. We show the 3D analysis technique developed for these data sets that forecast plasma velocity, density, and component magnetic fields at Earth, as well at the other inner heliospheric planets and spacecraft. One excellent coronal mass ejection (CME) example that occurred on the 10 March 2022 was viewed not only in the ISEE IPS analyses, but also by the spacecraft near Earth that measured the CME arrival at one AU. Solar Orbiter, that was nearly aligned along the Earth radial at 0.45 AU, also measured the CME in plasma density, velocity, and magnetic field. BepiColombo at 0.42 AU was also aligned with the STEREO A spacecraft, and viewed this CME. The instruments used here from BepiColombo include: 1) the European-Space-Agency Mercury-Planetary-Orbiter magnetic field measurements; 2) the Japan Aerospace Exploration Agency Mio spacecraft Solar Particle Monitor that viewed the CME Forbush decrease, and the Mercury Plasma Experiment/Mercury Electron Analyzer instruments that measured particles and solar-wind density from below the spacecraft protective sunshield covering. This article summarizes the analysis using ISEE, Japan real-time data for these forecasts: it provides a synopsis of the results and confirmation of the CME event morphology after its arrival, and discusses how future IPS analyses can augment these results.

    DOI: 10.1007/s11207-023-02169-8

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    Other Link: https://link.springer.com/article/10.1007/s11207-023-02169-8/fulltext.html

  2. Interplanetary Scintillation Observations of Solar-Wind Disturbances During Cycles 23 and 24 Reviewed

    Munetoshi Tokumaru, Ken'ichi Fujiki, Kazumasa Iwai

    SOLAR PHYSICS   Vol. 298 ( 2 )   2023.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    Interplanetary scintillation (IPS) analysis is an effective technique for remotely sensing solar-wind disturbances, such as stream-interaction regions (SIRs) and coronal mass ejections (CMEs), which are the main drivers of space weather. Here, we employed 327-MHz IPS observations conducted at the Institute of Space-Earth Environmental Research, Nagoya University for the period of 1997 - 2019 to determine IPS indices that represent the density-fluctuation level of the inner heliosphere. We then compared these indices with the solar-wind density and speed measured near the Earth. Consequently, we found weak but significant positive correlations between the IPS indices and both the solar-wind density and speed gradient at a time lag of 0 days. This suggests that an increase in IPS indices corresponds to the arrival of the compression region associated with SIR or CME at the Earth, which is consistent with model calculations. Significant negative correlations were observed between the IPS and disturbance storm time (Dst) indices at a time lag of a few days; however, the correlations were too weak to enable reliable predictions of space weather. Possible reasons for these weak correlations are also discussed. Using the IPS indices, we determined the solar-cycle variation in the occurrence rate of solar-wind disturbances for the analysis period. The occurrence rates exhibited two maxima corresponding to the solar maximum and minimum, which are generally consistent with the combined effects of CME and SIR. The lower occurrence rates in Cycle 24 than in Cycle 23 reflect a weaker solar activity. These results suggest that the proposed IPS indices are useful for studying the long-term characteristics of solar-wind disturbances.

    DOI: 10.1007/s11207-023-02116-7

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  3. Solar observing with the Atacama large millimeter-submillimeter array Reviewed

    T. S. Bastian, M. Shimojo, M. Bárta, S. M. White, K. Iwai

    Frontiers in Astronomy and Space Sciences   Vol. 9   2022.10

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    Publishing type:Research paper (scientific journal)   Publisher:Frontiers Media SA  

    The Atacama Large Millimeter-submillimeter Array (ALMA), sited on the high desert plains of Chajnantor in Chile, has opened a new window onto solar physics in 2016 by providing continuum observations at millimeter and sub-millimeter wavelengths with an angular resolution comparable to that available at optical (O), ultraviolet (UV), extreme ultraviolet (EUV), and X-ray wavelengths, and with superior time resolution. In the intervening years, progress has been made testing and commissioning new observing modes and capabilities, in developing data calibration strategies, and in data imaging and restoration techniques. Here we review ALMA current solar observing capabilities, the process by which a user may propose to use the instrument, and summarize the observing process and work flow. We then discuss some of the challenges users may encounter in imaging and analyzing their data. We conclude with a discussion of additional solar observing capabilities and modes under consideration that are intended to further exploit the unique spectral coverage provided by ALMA.

    DOI: 10.3389/fspas.2022.977368

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  4. Magnetohydrodynamic simulation of coronal mass ejections using interplanetary scintillation data observed from radio sites ISEE and LOFAR Reviewed

    Kazumasa Iwai, Richard A. Fallows, Mario M. Bisi, Daikou Shiota, Bernard V. Jackson, Munetoshi Tokumaru, Ken'ichi Fujiki

    Advances in Space Research     2022.9

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    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.asr.2022.09.028

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  5. Application of novel interplanetary scintillation visualisations using LOFAR: A case study of merged CMEs from September 2017 Reviewed

    R.A. Fallows, K. Iwai, B.V. Jackson, P. Zhang, M.M. Bisi, P. Zucca

    Advances in Space Research     2022.9

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    Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.asr.2022.08.076

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  6. Over seven decades of solar microwave data obtained with Toyokawa and Nobeyama Radio Polarimeters Reviewed

    Masumi Shimojo, Kazumasa Iwai

    Geoscience Data Journal     2022.6

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    Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    DOI: 10.1002/gdj3.165

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/gdj3.165

  7. Testing the Alfvén-wave Model of the Solar Wind with Interplanetary Scintillation Reviewed

    Munehito Shoda, Kazumasa Iwai, Daikou Shiota

    The Astrophysical Journal   Vol. 928 ( 2 ) page: 130 - 130   2022.4

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    Publishing type:Research paper (scientific journal)   Publisher:American Astronomical Society  

    Abstract

    Understanding the mechanism(s) of solar wind acceleration is important in astrophysics and geophysics. A promising model of solar wind acceleration is known as the wave/turbulence-driven (WTD) model, in which Alfvén waves feed energy to the solar wind. In this study, we tested the WTD model with global measurements of wind speed from interplanetary scintillation (IPS) observations. For Carrington rotations in minimal and maximal activity phases, we selected field lines calculated by the potential-field source-surface method in high and midlatitudes and compared the simulated and observed wind velocities. The simulation was performed in a self-consistent manner by solving the magnetohydrodynamic equations from the photosphere to the solar wind. In high-latitude regions, the simulated solar wind velocity agrees better with the IPS observation than with the classical Wang–Sheeley empirical estimation, both in maximal and minimal activity phases. In midlatitude regions, the agreement worsens, possibly because of the inaccuracy of the WTD model and/or the magnetic-field extrapolation. Our results indicate that the high-latitude solar wind is likely to be driven by waves and turbulence and that the physics-based prediction of the solar wind velocity is highly feasible with an improved magnetic-field extrapolation.

    DOI: 10.3847/1538-4357/ac581e

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    Other Link: https://iopscience.iop.org/article/10.3847/1538-4357/ac581e/pdf

  8. Global Distribution of the Solar Wind Speed Reconstructed from Improved Tomographic Analysis of Interplanetary Scintillation Observations between 1985 and 2019 Reviewed

    Munetoshi Tokumaru, Ken'ichi Fujiki, Masayoshi Kojima, Kazumasa Iwai

    ASTROPHYSICAL JOURNAL   Vol. 922 ( 1 )   2021.11

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    Computer-assisted tomography (CAT) for interplanetary scintillation (IPS) observations enables the determination of the global distribution of solar wind speed. We compared solar wind speeds derived from the CAT analysis of IPS observations between 1985 and 2019 with in situ observations conducted by the near-Earth and Ulysses spacecraft. From this comparison, we found that solar wind speeds from the IPS observations for 2009-2019 were systematically higher than the in situ observations, whereas those for the period until 2008 were in good agreement with the in situ observations. Further, we found that the discrepancy between IPS and the in situ observations is improved by changing the power index of the empirical relation between the solar wind speed and density fluctuations. The CAT analysis using an optimal value for the power index determined from the comparison between IPS and in situ observations revealed long-term variations in the solar wind speed distribution over three cycles, leading to a better understanding of the time-varying global heliosphere. We found that polar solar winds become highly anisotropic at the Cycle 24/25 minimum, which is a peculiar aspect of this minimum. The IPS observations showed general agreement with the Parker Solar Probe observations around the perihelion of Orbit 1; this supports the reliability of the CAT analysis. The results of this study suggest that the physical properties of solar wind microturbulence may vary with a long-term decline in the solar activity, which provides important implication on the solar wind acceleration.

    DOI: 10.3847/1538-4357/ac1862

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  9. BepiColombo’s Cruise Phase: Unique Opportunity for Synergistic Observations Reviewed

    L. Z. Hadid, V. Génot, S. Aizawa, A. Milillo, J. Zender, G. Murakami, J. Benkhoff, I. Zouganelis, T. Alberti, N. André, Z. Bebesi, F. Califano, A. P. Dimmock, M. Dosa, C. P. Escoubet, L. Griton, G. C. Ho, T. S. Horbury, K. Iwai, M. Janvier, E. Kilpua, B. Lavraud, A. Madar, Y. Miyoshi, D. Müller, R. F. Pinto, A. P. Rouillard, J. M. Raines, N. Raouafi, F. Sahraoui, B. Sánchez-Cano, D. Shiota, R. Vainio, A. Walsh

    Frontiers in Astronomy and Space Sciences   Vol. 8   2021.9

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    The investigation of multi-spacecraft coordinated observations during the cruise phase of BepiColombo (ESA/JAXA) are reported, with a particular emphasis on the recently launched missions, Solar Orbiter (ESA/NASA) and Parker Solar Probe (NASA). Despite some payload constraints, many instruments onboard BepiColombo are operating during its cruise phase simultaneously covering a wide range of heliocentric distances (0.28 AU–0.5 AU). Hence, the various spacecraft configurations and the combined in-situ and remote sensing measurements from the different spacecraft, offer unique opportunities for BepiColombo to be part of these unprecedented multipoint synergistic observations and for potential scientific studies in the inner heliosphere, even before its orbit insertion around Mercury in December 2025. The main goal of this report is to present the coordinated observation opportunities during the cruise phase of BepiColombo (excluding the planetary flybys). We summarize the identified science topics, the operational instruments, the method we have used to identify the windows of opportunity and discuss the planning of joint observations in the future.

    DOI: 10.3389/fspas.2021.718024

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  10. Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby Reviewed

    Martin Volwerk, Beatriz Sanchez-Cano, Daniel Heyner, Sae Aizawa, Nicolas Andre, Ali Varsani, Johannes Mieth, Stefano Orsini, Wolfgang Baumjohann, David Fischer, Yoshifumi Futaana, Richard Harrison, Harald Jeszenszky, Iwai Kazumasa, Gunter Laky, Herbert Lichtenegger, Anna Milillo, Yoshizumi Miyoshi, Rumi Nakamura, Ferdinand Plaschke, Ingo Richter, Sebastian Rojas Mata, Yoshifumi Saito, Daniel Schmid, Daikou Shiota, Cyril Simon Wedlund

    ANNALES GEOPHYSICAE   Vol. 39 ( 5 ) page: 811 - 831   2021.9

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the Yvso direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (SERENA-PICAM) of the SERENA suite, the Mercury Electron Analyser (MEA), and the BepiColombo Radiation Monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with e.g. strong flapping motions at a period of similar to 7 min This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.

    DOI: 10.5194/angeo-39-811-2021

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  11. PSTEP: project for solar-terrestrial environment prediction Reviewed

    Kanya Kusano, Kiyoshi Ichimoto, Mamoru Ishii, Yoshizumi Miyoshi, Shigeo Yoden, Hideharu Akiyoshi, Ayumi Asai, Yusuke Ebihara, Hitoshi Fujiwara, Tada-Nori Goto, Yoichiro Hanaoka, Hisashi Hayakawa, Keisuke Hosokawa, Hideyuki Hotta, Kornyanat Hozumi, Shinsuke Imada, Kazumasa Iwai, Toshihiko Iyemori, Hidekatsu Jin, Ryuho Kataoka, Yuto Katoh, Takashi Kikuchi, Yuki Kubo, Satoshi Kurita, Haruhisa Matsumoto, Takefumi Mitani, Hiroko Miyahara, Yasunobu Miyoshi, Tsutomu Nagatsuma, Aoi Nakamizo, Satoko Nakamura, Hiroyuki Nakata, Naoto Nishizuka, Yuichi Otsuka, Shinji Saito, Susumu Saito, Takashi Sakurai, Tatsuhiko Sato, Toshifumi Shimizu, Hiroyuki Shinagawa, Kazuo Shiokawa, Daikou Shiota, Takeshi Takashima, Chihiro Tao, Shin Toriumi, Satoru Ueno, Kyoko Watanabe, Shinichi Watari, Seiji Yashiro, Kohei Yoshida, Akimasa Yoshikawa

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.8

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    Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar-terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar-terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.

    DOI: 10.1186/s40623-021-01486-1

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  12. BepiColombo Science Investigations During Cruise and Flybys at the Earth, Venus and Mercury Reviewed

    Valeria Mangano, Melinda Dósa, Markus Fränz, Anna Milillo, Joana S. Oliveira, Yeon Joo Lee, Susan McKenna-Lawlor, Davide Grassi, Daniel Heyner, Alexander S. Kozyrev, Roberto Peron, Jörn Helbert, Sebastien Besse, Sara de la Fuente, Elsa Montagnon, Joe Zender, Martin Volwerk, Jean-Yves Chaufray, James A. Slavin, Harald Krüger, Alessandro Maturilli, Thomas Cornet, Kazumasa Iwai, Yoshizumi Miyoshi, Marco Lucente, Stefano Massetti, Carl A. Schmidt, Chuanfei Dong, Francesco Quarati, Takayuki Hirai, Ali Varsani, Denis Belyaev, Jun Zhong, Emilia K. J. Kilpua, Bernard V. Jackson, Dusan Odstrcil, Ferdinand Plaschke, Rami Vainio, Riku Jarvinen, Stavro Lambrov Ivanovski, Ákos Madár, Géza Erdős, Christina Plainaki, Tommaso Alberti, Sae Aizawa, Johannes Benkhoff, Go Murakami, Eric Quemerais, Harald Hiesinger, Igor G. Mitrofanov, Luciano Iess, Francesco Santoli, Stefano Orsini, Herbert Lichtenegger, Gunther Laky, Stas Barabash, Richard Moissl, Juhani Huovelin, Yasumasa Kasaba, Yoshifumi Saito, Masanori Kobayashi, Wolfgang Baumjohann

    Space Science Reviews   Vol. 217 ( 1 )   2021.2

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    Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    <title>Abstract</title>The dual spacecraft mission BepiColombo is the first joint mission between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) to explore the planet Mercury. BepiColombo was launched from Kourou (French Guiana) on October 20th, 2018, in its packed configuration including two spacecraft, a transfer module, and a sunshield. BepiColombo cruise trajectory is a long journey into the inner heliosphere, and it includes one flyby of the Earth (in April 2020), two of Venus (in October 2020 and August 2021), and six of Mercury (starting from 2021), before orbit insertion in December 2025. A big part of the mission instruments will be fully operational during the mission cruise phase, allowing unprecedented investigation of the different environments that will encounter during the 7-years long cruise. The present paper reviews all the planetary flybys and some interesting cruise configurations. Additional scientific research that will emerge in the coming years is also discussed, including the instruments that can contribute.

    DOI: 10.1007/s11214-021-00797-9

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    Other Link: http://link.springer.com/article/10.1007/s11214-021-00797-9/fulltext.html

  13. Validation of coronal mass ejection arrival-time forecasts by magnetohydrodynamic simulations based on interplanetary scintillation observations Reviewed

    Kazumasa Iwai, Daikou Shiota, Munetoshi Tokumaru, Ken’ichi Fujiki, Mitsue Den, Yûki Kubo

    Earth, Planets and Space   Vol. 73 ( 1 )   2021.1

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    <title>Abstract</title>Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME arrival times at the Earth forecasted by three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. In this system, CMEs are approximated as spheromaks with various initial speeds. Ten MHD simulations with different CME initial speed are tested, and the density distributions derived from each simulation run are compared with IPS data observed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University. The CME arrival time of the simulation run that most closely agrees with the IPS data is selected as the forecasted time. We then validated the accuracy of this forecast using 12 halo CME events. The average absolute arrival-time error of the IPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereas that of MHD simulations without IPS data, in which the initial CME speed is derived from white-light coronagraph images, is approximately 6.7 h. This suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. The average predicted arrival times are earlier than the actual arrival times. These early predictions may be due to overestimation of the magnetic field included in the spheromak and/or underestimation of the drag force from the background solar wind, the latter of which could be related to underestimation of CME size or background solar wind density.

    DOI: 10.1186/s40623-020-01345-5

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    Other Link: http://link.springer.com/article/10.1186/s40623-020-01345-5/fulltext.html

  14. Estimating the Temperature and Density of a Spicule from 100 GHz Data Obtained with ALMA Reviewed

    Masumi Shimojo, Tomoko Kawate, Takenori J. Okamoto, Takaaki Yokoyama, Noriyuki Narukage, Taro Sakao, Kazumasa Iwai, Gregory D. Fleishman, Kazunari Shibata

    The Astrophysical Journal   Vol. 888 ( 2 )   2020.1

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    DOI: 10.3847/2041-8213/ab62a5

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  15. Spectral Structures of Type II Solar Radio Bursts and Solar Energetic Particles Reviewed International coauthorship International journal

    Iwai, Kazumasa, Yashiro, Seiji, Nitta, Nariaki, V, Kubo, Yuki

    ASTROPHYSICAL JOURNAL   Vol. 888 ( 1 )   2020.1

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

    We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SEPs). To examine the statistical relationship between type II bursts and SEPs, we selected 26 coronal mass ejection (CME) events with similar characteristics (e.g., initial speed, angular width, and location) observed by the Large Angle and Spectrometric Coronagraph, regardless of the characteristics of the corresponding type II bursts and the SEP flux. Then, we compared associated type II bursts observed by the Radio and Plasma Wave Experiment on board the Wind spacecraft and the SEP flux observed by the Geostationary Operational Environmental Satellite orbiting around the Earth. We found that the bandwidth of the hectometric type II bursts and the peak flux of the SEPs has a positive correlation (with a correlation coefficient of 0.64). This result supports the idea that the nonthermal electrons of type II bursts and the nonthermal ions of SEPs are generated by the same shock and suggests that more SEPs may be generated for a wider or stronger CME shock with a longer duration. Our result also suggests that considering the spectral structures of type II bursts can improve the forecasting accuracy for the peak flux of gradual SEPs.

    DOI: 10.3847/1538-4357/ab57ff

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  16. Coordinated Interplanetary Scintillation Observations in Japan and Russia for Coronal Mass Ejection Events in Early September 2017 Reviewed

    Tokumaru, Munetoshi, Fujiki, Ken'ichi, Iwai, Kazumasa, Tyul'bashev, Sergey, Chashei, Igor

    SOLAR PHYSICS   Vol. 294 ( 7 )   2019.7

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    Interplanetary (IP) shocks traveling between the Sun and the Earth's orbit were clearly detected in interplanetary scintillation (IPS) observations made at Toyokawa (Japan) and Pushchino (Russia), in association with two halo coronal mass ejections (CMEs) that occurred on 04 and 06 September 2017. Since the observation times at Toyokawa and Pushchino differ by about six hours, a combined analysis of the IPS data obtained at these sites enabled high-cadence tracking of the IP shock for one of the CME events. The plane-of-sky locations where the IP disturbances were observed at Toyokawa were generally consistent with those at Pushchino. The propagation speeds of IP shocks inferred from IPS observations were higher than the average speeds derived from the occurrence time of IP shocks at Earth. This difference was ascribed to the deceleration of the CME-driven shocks during propagation. The east-west asymmetry of the propagation speed of IP shocks was also revealed from IPS observations. Solar-wind disturbances moving at a speed significantly slower than the average speed of the IP shock were identified from the IPS observations of the 06 September 2017 halo CME event. A wide longitudinal extent of these slow disturbances was suggested by the fact they were observed not only west but also east of the Sun; i.e. the opposite side to the flare/CME site. The origin of the slow disturbances is considered to represent either wing portions of the highly warped IP shock or the post-shock dense materials.

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  17. Development of a coronal mass ejection arrival time forecasting system using interplanetary scintillation observations Reviewed

    Iwai Kazumasa, Shiota Daikou, Tokumaru Munetoshi, Fujiki Ken'ichi, Den Mitsue, Kubo Yuki

    EARTH PLANETS AND SPACE   Vol. 71   2019.4

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    Coronal mass ejections (CMEs) cause disturbances in the environment of the Earth when they arrive at the Earth. However, the prediction of the arrival of CMEs still remains a challenge. We have developed an interplanetary scintillation (IPS) estimation system based on a global magnetohydrodynamic (MHD) simulation of the inner heliosphere to predict the arrival time of CMEs. In this system, the initial speed of a CME is roughly derived from white-light coronagraph observations. Then, the propagation of the CME is calculated by a global MHD simulation. The IPS response is estimated by the three-dimensional density distribution of the inner heliosphere derived from the MHD simulation. The simulated IPS response is compared with the actual IPS observations made by the Institute for Space-Earth Environmental Research, Nagoya University, and shows good agreement with that observed. We demonstrated how the simulation system works using a halo CME event generated by a X9.3 flare observed on September 5, 2017. We find that the CME simulation that best estimates the IPS observation can more accurately predict the time of arrival of the CME at the Earth. These results suggest that the accuracy of the CME arrival time can be improved if our current MHD simulations include IPS data.

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  18. Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles Reviewed

    Fujiki Ken'ichi, Shibasaki Kiyoto, Yashiro Seiji, Tokumaru Munetoshi, Iwai Kazumasa, Masuda Satoshi

    SOLAR PHYSICS   Vol. 294 ( 3 )   2019.3

  19. Solar Polar Brightening and Radius at 100 and 230GHz Observed by ALMA Reviewed

    Selhorst Caius L, Simoes Paulo J. A, Brajsa Roman, Valio Adriana, Gimenez de, Castro C. G, Costa Joaquim E. R, Menezes Fabian, Pierre Rozelot Jean, Hales Antonio S, Iwai Kazumasa, White Stephen

    ASTROPHYSICAL JOURNAL   Vol. 871 ( 1 )   2019.1

  20. Detection of Propagating Fast Sausage Waves through Detailed Analysis of a Zebra-pattern Fine Structure in a Solar Radio Burst Reviewed

    K. Kaneda, H. Misawa, K. Iwai, S. Masuda, F. Tsuchiya, Y. Katoh, T. Obara

    Astrophysical Journal Letters   Vol. 855 ( 2 )   2018.3

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    Various magnetohydrodynamic (MHD) waves have recently been detected in the solar corona and investigated intensively in the context of coronal heating and coronal seismology. In this Letter, we report the first detection of short-period propagating fast sausage mode waves in a metric radio spectral fine structure observed with the Assembly of Metric-band Aperture Telescope and Real-time Analysis System. Analysis of Zebra patterns (ZPs) in a type-IV burst revealed a quasi-periodic modulation in the frequency separation between the adjacent stripes of the ZPs (Δf ). The observed quasi-periodic modulation had a period of 1-2 s and exhibited a characteristic negative frequency drift with a rate of 3-8 MHz s-1. Based on the double plasma resonance model, the most accepted generation model of ZPs, the observed quasi-periodic modulation of the ZP can be interpreted in terms of fast sausage mode waves propagating upward at phase speeds of 3000-8000 km s-1. These results provide us with new insights for probing the fine structure of coronal loops.

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  21. Solar ALMA Observations: Constraining the Chromosphere above Sunspots Reviewed

    Maria A. Loukitcheva, Kazumasa Iwai, Sami K. Solanki, Stephen M. White, Masumi Shimojo

    ASTROPHYSICAL JOURNAL   Vol. 850 ( 1 )   2017.11

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    We present the first high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a sunspot at wavelengths of 1.3 and 3 mm, obtained during the solar ALMA Science Verification campaign in 2015, and compare them with the predictions of semi-empirical sunspot umbral/penumbral atmosphere models. For the first time, millimeter observations of sunspots have resolved umbral/penumbral brightness structure at the chromospheric heights, where the emission at these wavelengths is formed. We find that the sunspot umbra exhibits a radically different appearance at 1.3 and 3 mm, whereas the penumbral brightness structure is similar at the two wavelengths. The inner part of the umbra is similar to 600 K brighter than the surrounding quiet Sun (QS) at 3 mm and is similar to 700 K cooler than the QS at 1.3 mm, being the coolest part of sunspot at this wavelength. On average, the brightness of the penumbra at 3 mm is comparable to the QS brightness, while at 1.3 mm it is similar to 1000 K brighter than the QS. Penumbral brightness increases toward the outer boundary in both ALMA bands. Among the tested umbral models, that of Severino et al. provides the best fit to the observational data, including both the ALMA data analyzed in this study and data from earlier works. No penumbral model among those considered here gives a satisfactory fit to the currently available measurements. ALMA observations at multiple millimeter wavelengths can be used for testing existing sunspot models, and serve as an important input to constrain new empirical models.

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  22. Variation of the Solar Microwave Spectrum in the Last Half Century Reviewed

    Masumi Shimojo, Kazumasa Iwai, Ayumi Asai, Satoshi Nozawa, Tetsuhiro Minamidani, Masao Saito

    ASTROPHYSICAL JOURNAL   Vol. 848 ( 1 )   2017.10

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    The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed continuously from 1957 to 1994 at Toyokawa, Japan, and from 1994 until now at Nobeyama, Japan, with the current Nobeyama Radio Polarimeters. We examined the multi-frequency and long-term data sets, and found that not only the microwave solar flux but also its monthly standard deviation indicate the long-term variation of solar activity. Furthermore, we found that the microwave spectra at the solar minima of Cycles 20-24 agree with each other. These results show that the average atmospheric structure above the upper chromosphere in the quiet-Sun has not varied for half a century, and suggest that the energy input for atmospheric heating from the sub-photosphere to the corona have not changed in the quiet-Sun despite significantly differing strengths of magnetic activity in the last five solar cycles.

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  23. OCTAD-S: digital fast Fourier transform spectrometers by FPGA Reviewed

    Kazumasa Iwai, Yuki Kubo, Hiromitsu Ishibashi, Takahiro Naoi, Kenichi Harada, Kenji Ema, Yoshinori Hayashi, Yuichi Chikahiro

    EARTH PLANETS AND SPACE   Vol. 69   page: 95   2017.7

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    We have developed a digital fast Fourier transform spectrometer made of an analog-to-digital converter (ADC) and a field-programmable gate array (FPGA). The base instrument has independent ADC and FPGA modules, which allow us to implement different spectrometers in a relatively easy manner. Two types of spectrometers have been instrumented: one with 4.096 GS/s sampling speed and 2048 frequency channels and the other with 2.048 GS/s sampling speed and 32,768 frequency channels. The signal processing in these spectrometers has no dead time, and the accumulated spectra are recorded in external media every 8 ms. A direct sampling spectroscopy up to 8 GHz is achieved by a microwave track-and-hold circuit, which can reduce the analog receiver in front of the spectrometer. Highly stable spectroscopy with a wide dynamic range was demonstrated in a series of laboratory experiments and test observations of solar radio bursts.

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  24. Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping Reviewed

    S. M. White, K. Iwai, N. M. Phillips, R. E. Hills, A. Hirota, P. Yagoubov, G. Siringo, M. Shimojo, T. S. Bastian, A. S. Hales, T. Sawada, S. Asayama, M. Sugimoto, R. G. Marson, W. Kawasaki, E. Muller, T. Nakazato, K. Sugimoto, R. Brajsa, I. Skokic, M. Barta, S. Kim, A. J. Remijan, I. de Gregorio, S. A. Corder, H. S. Hudson, M. Loukitcheva, B. Chen, B. De Pontieu, G. D. Fleishmann, D. E. Gary, A. Kobelski, S. Wedemeyer, Y. Yan

    SOLAR PHYSICS   Vol. 292 ( 7 )   2017.7

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    The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at lambda = 3 mm and 5900 K at lambda = 1.3 mm. These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about 25 '', the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images.

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  25. ALMA Discovery of Solar Umbral Brightness Enhancement at lambda=3 mm Reviewed International coauthorship International journal

    Kazumasa Iwai, Maria Loukitcheva, Masumi Shimojo, Sami K. Solanki, Stephen M. White

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 841 ( 2 ) page: L20   2017.6

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    We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a lambda = 3 mm (100 GHz) mosaic image obtained by ALMA that includes a large sunspot within the active region AR12470, on 2015 December 16. The 3 mm map has a 300 '' x 300 '' field of view and 4 ''.9 x 2 ''.2 spatial resolution, which is the highest spatial resolution map of an entire sunspot in this frequency range. We find a gradient of 3 mm brightness from a high value in the outer penumbra to a low value in the inner penumbra/outer umbra. Within the inner umbra, there is a marked increase in 3 mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightness in the 1330 and 1400 angstrom slit-jaw images of the Interface Region Imaging Spectrograph (IRIS), adjacent to a partial lightbridge. This lambda = 3 mm brightness enhancement may be an intrinsic feature of the sunspot umbra at chromospheric heights, such as a manifestation of umbral flashes, or it could be related to a coronal plume, since the brightness enhancement was coincident with the footpoint of a coronal loop observed at 171 angstrom.

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  26. Polarization Characteristics of Zebra Patterns in Type IV Solar Radio Bursts Reviewed

    K. Kaneda, H. Misawa, K. Iwai, F. Tsuchiya, T. Obara, Y. Katoh, S. Masuda

    ASTROPHYSICAL JOURNAL   Vol. 842 ( 1 )   2017.6

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    The polarization characteristics of zebra patterns (ZPs) in type IV solar bursts were studied. We analyzed 21 ZP events observed by the. Assembly of Metric-band Aperture Telescope and Real-time Analysis System between 2010 and 2015 and identified the following characteristics: a degree of circular polarization (DCP) in the range of 0%-70%, a temporal delay of 0-70 ms between the two circularly polarized components (i.e., the right- and left-handed components), and dominant ordinary-mode emission in about 81% of the events. For most events, the relation between the dominant and delayed components could be interpreted in the framework of fundamental plasma emission and depolarization during propagation, though the values of DCP and delay were distributed across wide ranges. Furthermore, it was found that the DCP and delay were positively correlated (rank correlation coefficient R = 0.62). As a possible interpretation of this relationship, we considered a model based on depolarization due to reflections at sharp density boundaries assuming fundamental plasma emission. The model calculations of depolarization including multiple reflections and group delay during propagation in the inhomogeneous corona showed that the DCP and delay decreased as the number of reflections increased, which is consistent with the observational results. The dispersive polarization characteristics could be explained by the different numbers of reflections causing depolarization.

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  27. The First ALMA Observation of a Solar Plasmoid Ejection from an X-Ray Bright Point Reviewed International coauthorship International journal

    Masumi Shimojo, Hugh S. Hudson, Stephen M. White, Timothy S. Bastian, Kazumasa Iwai

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 841 ( 1 )   2017.5

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    Eruptive phenomena such as plasmoid ejections or jets are important features of solar activity and have the potential to improve our understanding of the dynamics of the solar atmosphere. Such ejections are often thought to be signatures of the outflows expected in regions of fast magnetic reconnection. The 304 angstrom EUV line of helium, formed at around 10(5) K, is found to be a reliable tracer of such phenomena, but the determination of physical parameters from such observations is not straightforward. We have observed a plasmoid ejection from an X-ray bright point simultaneously at millimeter wavelengths with ALMA, at EUV wavelengths with SDO/AIA, and in soft X-rays with Hinode/XRT. This paper reports the physical parameters of the plasmoid obtained by combining the radio, EUV, and X-ray data. As a result, we conclude that the plasmoid can consist either of (approximately) isothermal similar to 10(5) K plasma that is optically thin at 100 GHz, or a similar to 10(4) K core with a hot envelope. The analysis demonstrates the value of the additional temperature and density constraints that ALMA provides, and future science observations with ALMA will be able to match the spatial resolution of space-borne and other high-resolution telescopes.

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  28. The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm Reviewed International coauthorship International journal

    Kazumasa Iwai, Masumi Shimojo, Shinichiro Asayama, Tetsuhiro Minamidani, Stephen White, Timothy Bastian, Masao Saito

    SOLAR PHYSICS   Vol. 292 ( 1 ) page: 22   2017.1

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    The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor-insulator-superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is 7700 +/- 310 K at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations.

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  29. Microwave observations of a large-scale coronal wave with the Nobeyama radioheliograph Reviewed

    A. Warmuth, K. Shibasaki, K. Iwai, G. Mann

    ASTRONOMY & ASTROPHYSICS   Vol. 593   2016.9

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    Context. Large-scale globally propagating waves in the solar corona have been studied extensively, mainly using extreme ultraviolet (EUV) observations. In a few events, corresponding wave signatures have been detected in microwave radioheliograms provided by the Nobeyama radioheliograph (NoRH). Several aspects of these observations seem to contradict the conclusions drawn from EUV observations.
    Aims. We investigate whether the microwave observations of global waves are consistent with previous findings.
    Methods. We revisited the wave of 1997 Sep. 24, which is still the best-defined event in microwaves. We obtained radioheliograms at 17 and 34 GHz from NoRH and studied the morphology, kinematics, perturbation profile evolution, and emission mechanism of the propagating microwave signatures.
    Results. We find that the NoRH wave signatures are morphologically consistent with both the associated coronal wave as observed by SOHO/EIT and the Moreton wave seen in H alpha. The NoRH wave is clearly decelerating, which is typically found for large-amplitude coronal waves associated with Moreton waves, and its kinematical curve is consistent with the EIT wavefronts. The perturbation profile shows a pronounced decrease in amplitude. Based on the derivation of the spectral index of the excess microwave emission, we conclude that the NoRH wave is due to optically thick free-free bremsstrahlung from the chromosphere.
    Conclusions. The wavefronts seen in microwave radioheliograms are chromospheric signatures of coronal waves, and their characteristics support the interpretation of coronal waves as large-amplitude fast-mode MHD waves or shocks.

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  30. CORONAL MAGNETIC FIELDS DERIVED FROM SIMULTANEOUS MICROWAVE AND EUV OBSERVATIONS AND COMPARISON WITH THE POTENTIAL FIELD MODEL Reviewed

    Shun Miyawaki, Kazumasa Iwai, Kiyoto Shibasaki, Daikou Shiota, Satoshi Nozawa

    ASTROPHYSICAL JOURNAL   Vol. 818 ( 1 )   2016.2

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    We estimated the accuracy of coronal magnetic fields derived from radio observations by comparing them to potential field calculations and the differential emission measure measurements using EUV observations. We derived line-of-sight components of the coronal magnetic field from polarization observations of the thermal bremsstrahlung in the NOAA active region 11150, observed around 3:00 UT on 2011 February 3 using the Nobeyama Radioheliograph at 17 GHz. Because the thermal bremsstrahlung intensity at 17 GHz includes both chromospheric and coronal components, we extracted only the coronal component by measuring the coronal emission measure in EUV observations. In addition, we derived only the radio polarization component of the corona by selecting the region of coronal loops and weak magnetic field strength in the chromosphere along the line of sight. The upper limits of the coronal longitudinal magnetic fields were determined as 100-210 G. We also calculated the coronal longitudinal magnetic fields from the potential field extrapolation using the photospheric magnetic field obtained from the Helioseismic and Magnetic Imager. However, the calculated potential fields were certainly smaller than the observed coronal longitudinal magnetic field. This discrepancy between the potential and the observed magnetic field strengths can be explained consistently by two reasons:. (1) the underestimation of the coronal emission measure resulting from the limitation of the temperature range of the EUV observations, and (2) the underestimation of the coronal magnetic field resulting from the potential field assumption.

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  31. CHROMOSPHERIC SUNSPOTS IN THE MILLIMETER RANGE AS OBSERVED BY THE NOBEYAMA RADIOHELIOGRAPH Reviewed

    Kazumasa Iwai, Hideki Koshiishi, Kiyoto Shibasaki, Satoshi Nozawa, Shun Miyawaki, Takuro Yoneya

    ASTROPHYSICAL JOURNAL   Vol. 816 ( 2 ) page: 91   2016.1

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    We investigate the upper chromosphere and the transition region of the sunspot umbra using the radio brightness temperature at 34 GHz (corresponding to 8.8 mm observations) as observed by the Nobeyama Radioheliograph (NoRH). Radio free-free emission in the longer millimeter range is generated around the transition region, and its brightness temperature yields the region's temperature and density distribution. We use the NoRH data at 34 GHz by applying the Steer-CLEAN image synthesis. These data and the analysis method enable us to investigate the chromospheric structures in the longer millimeter range with high spatial resolution and sufficient visibilities. We also perform simultaneous observations of one sunspot using the NoRH and the Nobeyama 45 m telescope operating at 115 GHz. We determine that 115 GHz emission mainly originates from the lower chromosphere while 34 GHz emission mainly originates from the upper chromosphere and transition region. These observational results are consistent with the radio emission characteristics estimated from current atmospheric models of the chromosphere. On the other hand, the observed brightness temperature of the umbral region is almost the same as that of the quiet region. This result is inconsistent with current sunspot models, which predict a considerably higher brightness temperature of the sunspot umbra at 34 GHz. This inconsistency suggests that the temperature of the region at which the 34 GHz radio emission becomes optically thick should be lower than that predicted by the models.

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  32. FREQUENCY DEPENDENCE OF POLARIZATION OF ZEBRA PATTERN IN TYPE-IV SOLAR RADIO BURSTS Reviewed

    Kazutaka Kaneda, H. Misawa, K. Iwai, F. Tsuchiya, T. Obara

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 808 ( 2 )   2015.8

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    We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZPs. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50%-70% right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50-70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double-plasma-resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.

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  33. SOLAR MICRO-TYPE III BURST STORMS AND LONG DIPOLAR MAGNETIC FIELD IN THE OUTER CORONA Reviewed

    A. Morioka, Y. Miyoshi, K. Iwai, Y. Kasaba, S. Masuda, H. Misawa, T. Obara

    ASTROPHYSICAL JOURNAL   Vol. 808 ( 2 )   2015.8

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    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 R-S. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

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  34. OBSERVATION OF THE CHROMOSPHERIC SUNSPOT AT MILLIMETER RANGE WITH THE NOBEYAMA 45 m TELESCOPE Reviewed

    Kazumasa Iwai, Masumi Shimojo

    ASTROPHYSICAL JOURNAL   Vol. 804 ( 1 ) page: 48   2015.5

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    The brightness temperature of the radio free-free emission at millimeter range is an effective tool for characterizing the vertical structure of the solar chromosphere. In this paper, we report on the first single-dish observation of a sunspot at 85 and 115 GHz with sufficient spatial resolution for resolving the sunspot umbra using the Nobeyama 45 m telescope. We used radio attenuation material, i.e., a solar filter, to prevent the saturation of the receivers. Considering the contamination from the plage by the side lobes, we found that the brightness temperature of the umbra should be lower than that of the quiet region. This result is inconsistent with the preexisting atmospheric models. We also found that the brightness temperature distribution at millimeter range strongly corresponds to the ultraviolet continuum emission at 1700 angstrom, especially at the quiet region.

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  35. Coronal magnetic field and the plasma beta determined from radio and multiple satellite observations Invited Reviewed

    Iwai Kazumasa, Shibasaki, K., Nozawa, S., Takahashi, T., Sawada, S., Kitagawa, J., Miyawaki, S. and Kashiwagi, H.

    Earth Planets and Space   Vol. 66   page: 149   2014.11

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    DOI: 10.1186/s40623-014-0149-z

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  36. SPECTRAL STRUCTURES AND THEIR GENERATION MECHANISMS FOR SOLAR RADIO TYPE-I BURSTS Reviewed

    K. Iwai, Y. Miyoshi, S. Masuda, F. Tsuchiya, A. Morioka, H. Misawa

    ASTROPHYSICAL JOURNAL   Vol. 789 ( 1 ) page: 4   2014.7

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    The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATERAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there was no similarity in the shapes of the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by nonthermal electrons is modulated in the subsequent stages of the generation of nonthermal electrons, such as plasma wave generation, radio wave emissions, and propagation. The variation of the timescale of the growth rate is significantly larger than that of the coronal environments. These results can be explained by the situation wherein the source region may have the inhomogeneity of an ambient plasma environment, such as the boundary of open and closed field lines, and the superposition of entire emitted bursts was observed by the spectrometer.

    DOI: 10.1088/0004-637X/789/1/4

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  37. GENERATION MECHANISM OF THE SLOWLY DRIFTING NARROWBAND STRUCTURE IN THE TYPE IV SOLAR RADIO BURSTS OBSERVED BY AMATERAS Reviewed

    Y. Katoh, K. Iwai, Y. Nishimura, A. Kumamoto, H. Misawa, F. Tsuchiya, T. Ono

    ASTROPHYSICAL JOURNAL   Vol. 787 ( 1 )   2014.5

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    We investigate the type IV burst event observed by AMATERAS on 2011 June 7, and reveal that the main component of the burst was emitted from the plasmoid eruption identified in the EUV images of the Solar Dynamics Observatory (SDO)/AIA. We show that a slowly drifting narrowband structure (SDNS) appeared in the burst's spectra. Using statistical analysis, we reveal that the SDNS appeared for a duration of tens to hundreds of milliseconds and had a typical bandwidth of 3 MHz. To explain the mechanism generating the SDNS, we propose wave-wave coupling between Langmuir waves and whistler-mode chorus emissions generated in a post-flare loop, which were inferred from the similarities in the plasma environments of a post-flare loop and the equatorial region of Earth's inner magnetosphere. We assume that a chorus element with a rising tone is generated at the top of a post-flare loop. Using the magnetic field and plasma density models, we quantitatively estimate the expected duration of radio emissions generated from coupling between Langmuir waves and chorus emissions during their propagation in the post-flare loop, and we find that the observed duration and bandwidth properties of the SDNS are consistently explained by the proposed generation mechanism. While observations in the terrestrial magnetosphere show that the chorus emissions are a group of large-amplitude wave elements generated naturally and intermittently, the mechanism proposed in the present study can explain both the intermittency and the frequency drift in the observed spectra.

    DOI: 10.1088/0004-637X/787/1/45

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  38. Measurements of Coronal and Chromospheric Magnetic Fields Using Polarization Observations by the Nobeyama Radioheliograph Reviewed

    Kazumasa Iwai, Kiyoto Shibasaki

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   Vol. 65 ( SP1 ) page: S14   2013.12

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    Coronal and chromospheric magnetic fields are derived from polarization and spectral observations of the thermal free free emission using the Nobeyama Radioheliograph (NoRH). In magnetized plasma, the ordinary and extraordinary modes of free free emission have different optical depths. This creates a circularly polarized component in an atmosphere with a temperature gradient. We observed an active region on 2012 April 13 to derive its coronal and chromospheric magnetic fields. The observed degree of circular polarization was between 0.5% and 1.7%. The radio circular polarization images were compared with ultraviolet images observed by the Atmospheric Imaging Assembly and the photospheric magnetic field observed by the Helioseismic and Magnetic Imager, both on board the Solar Dynamic Observatory. At the edge of the active region, the radio circular polarization was emitted mainly from coronal loops, and the coronal magnetic field was derived to be about 70 G. At the center of the active region, the chromospheric and coronal components cannot be separated. The derived magnetic field is about 20% to 50% of the corresponding photospheric magnetic field, which is an emission-measure-weighted average of the coronal and chromospheric magnetic fields.

    DOI: 10.1093/pasj/65.sp1.S14

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  39. PEAK FLUX DISTRIBUTIONS OF SOLAR RADIO TYPE-I BURSTS FROM HIGHLY RESOLVED SPECTRAL OBSERVATIONS Reviewed

    K. Iwai, S. Masuda, Y. Miyoshi, F. Tsuchiya, A. Morioka, H. Misawa

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 768 ( 1 ) page: L2   2013.5

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    Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations with the radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a two-dimensional auto burst detection algorithm that can distinguish each type-I burst element from complex noise storm spectra that include numerous instances of radio frequency interference (RFI). This algorithm removes RFI from the observed radio spectra by applying a moving median filter along the frequency axis. Burst and continuum components are distinguished by a two-dimensional maximum and minimum search of the radio dynamic spectra. The analysis result shows that each type-I burst element has one peak flux without double counts or missed counts. The peak flux distribution of type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and 5.

    DOI: 10.1088/2041-8205/768/1/L2

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  40. IPRT/AMATERAS: A New Metric Spectrum Observation System for Solar Radio Bursts Reviewed

    K. Iwai, F. Tsuchiya, A. Morioka, H. Misawa

    SOLAR PHYSICS   Vol. 277 ( 2 ) page: 447 - 457   2012.4

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    A new radio spectropolarimeter for solar radio observation has been developed at Tohoku University and installed on the Iitate Planetary Radio Telescope (IPRT) at the Iitate observatory in Fukushima prefecture, Japan. This system, named AMATERAS (the Assembly of Metric-band Aperture TElescope and Real-time Analysis System), enables us to observe solar radio bursts in the frequency range between 150 and 500 MHz. The minimum detectable flux in the observation frequency range is less than 0.7 SFU with an integration time of 10 ms and a bandwidth of 61 kHz. Both left and right polarization components are simultaneously observed in this system. These specifications are accomplished by combining the large aperture of IPRT with a high-speed digital receiver. Observational data are calibrated and archived soon after the daily observation. The database is available online. The high-sensitivity observational data with the high time and frequency resolutions from AMATERAS will be used to analyze spectral fine structures of solar radio bursts.

    DOI: 10.1007/s11207-011-9919-y

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  41. SOLAR RADIO TYPE-I NOISE STORM MODULATED BY CORONAL MASS EJECTIONS Reviewed

    K. Iwai, Y. Miyoshi, S. Masuda, M. Shimojo, D. Shiota, S. Inoue, F. Tsuchiya, A. Morioka, H. Misawa

    ASTROPHYSICAL JOURNAL   Vol. 744 ( 2 ) page: 167   2012.1

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    The first coordinated observations of an active region using ground-based radio telescopes and the Solar Terrestrial Relations Observatory (STEREO) satellites from different heliocentric longitudes were performed to study solar radio type-I noise storms. A type-I noise storm was observed between 100 and 300 MHz during a period from 2010 February 6 to 7. During this period the two STEREO satellites were located approximately 65. (ahead) and -70 degrees (behind) from the Sun-Earth line, which is well suited to observe the earthward propagating coronal mass ejections (CMEs). The radio flux of the type-I noise storm was enhanced after the preceding CME and began to decrease before the subsequent CME. This time variation of the type-I noise storm was directly related to the change of the particle acceleration processes around its source region. Potential-field source-surface extrapolation from the Solar and Heliospheric Observatory/ Michelson Doppler Imager (SOHO/ MDI) magnetograms suggested that there was a multipolar magnetic system around the active region from which the CMEs occurred around the magnetic neutral line of the system. From our observational results, we suggest that the type-I noise storm was activated at a side-lobe reconnection region that was formed after eruption of the preceding CME. This magnetic structure was deformed by a loop expansion that led to the subsequent CME, which then suppressed the radio burst emission.

    DOI: 10.1088/0004-637X/744/2/167

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Books 2

  1. Solar-terrestrial environmental prediction

    Kusano, Kanya(Structure of Solar Atmosphere and Magnetic Phenomena)

    Springer  2023.2  ( ISBN:9789811977640

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    Total pages:xxiv, 462 p.   Language:English

    CiNii Books

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  2. PSTEP Open Textbook

    ( Role: Contributor)

    2021.8 

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MISC 10

  1. Database of Solar Radio Bursts Observed by Solar Radio Spectro-polarimeter AMATERAS Reviewed

    Tsuchiya, F, H. Misawa, T. Obara, K. Iwai, K. Kaneda, S. Matsumoto, A. Kumamoto, Y. Katoh, M. Yagi, B. Cecconi

    Planetary Radio Emission 8     page: 445 - 453   2017

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    Language:English   Publishing type:Article, review, commentary, editorial, etc. (international conference proceedings)  

    DOI: 10.1553/PRE8s445

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  2. An FFT Circuit for a Spectrometer of a Radio Telescope using the Nested RNS including the Constant Division. Reviewed

    Hiroki Nakahara, Hiroyuki Nakanishi, Kazumasa Iwai, Tsutomu Sasao

    SIGARCH Computer Architecture News   Vol. 44 ( 4 ) page: 44 - 49   2016

  3. An FFT Circuit Using Nested RNS in a Digital Spectrometer for a Radio Telescope Reviewed

    Hiroki Nakahara, Tsutomu Sasao, Hiroyuki Nakanishi, Kazumasa Iwai, Tohru Nagao, Naoya Ogawa

    2016 IEEE 46TH INTERNATIONAL SYMPOSIUM ON MULTIPLE-VALUED LOGIC (ISMVL 2016)     page: 60 - 65   2016

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    Language:English   Publisher:IEEE COMPUTER SOC  

    A radio telescope analyzes radio frequency (RF) signal received from celestial objects. It consists of an antenna, a receiver, and a spectrometer. The spectrometer converts the time domain signal into the frequency domain signal by an FFT operation. This paper proposes an FFT circuit based on nested residue number system (NRNS). Since the FFT operation is the most computationally intensive part, parallel implementation is necessary to realize a high-speed FFT. We used an FPGA to implement the circuit. The FPGA consists of look-up tables (LUTs) and block RAMs (BRAMs). For direct parallel FFT realization using an existing FPGA library, the number of LUTs for the complex multipliers is the bottleneck. To reduce the number of LUTs in an FPGA, we increase the dynamic range stage by stage. In this case, NRNS2NRNS converters that convert smaller dynamic range to larger dynamic range are necessary. We implemented the proposed NRNS FFT on the Xilinx Corp. Virtex 7 FPGA. Compared with a conventional binary FFT, although the number of block RAMs (BRAMs) was increased by 20.0-156.5%, in the RNS FFT, the number of LUTs was decreased by 42.4-47.8% and the maximum clock frequency was increased by 9.3-41.7%. With this technique, we successfully implemented an FFT that satisfied the required size and speed specifications on an available FPGA, since the excessive number of LUTs was the bottleneck of the binary FFT.

    DOI: 10.1109/ISMVL.2016.35

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  4. An RNS FFT Circuit Using LUT Cascades Based on a Modulo EVMDD Reviewed

    Hiroki Nakahara, Tsutomu Sasao, Hiroyuki Nakanishi, Kazumasa Iwai

    Proceedings of The International Symposium on Multiple-Valued Logic   Vol. 2015-September   page: 97 - 102   2015.9

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    Language:English   Publisher:IEEE Computer Society  

    This paper proposes an FFT circuit based on aresidue number system (RNS) using LUT cascades. To reduce the number of look-up tables (LUTs) in an FPGA, we usedtwo techniques. The first one is the functional decomposition of multipliers using RNS. The second one is the increase of the dynamic range stage by stage. The circuit requires the RNS2RNSconverter which converts a small dynamic range to a large dynamic range. To compactly realize the RNS2RNS converter, we decompose it into an RNS2Binary converter and a Binary2RNSconverter. Although the Binary2RNS converter can be realized by an LUT cascade based on a multi-terminal multi-valued decision diagram (MTMDD), the RNS2Binary converter tend tube large for the conventional circuit. Thus, we introduce an LUTcascade based on a modulo edge-valued multi-valued decision diagram (mod-EVMDD). The mod-EVMDD is a new type of a decision diagram that efficiently represents the RNS2Binaryconverter. We implemented the proposed RNS FFT on the Xilinx Corp. Virtex 6 FPGA. Compared with the conventional binary FFT implementation, although the number of blockRAMs (BRAMs) increased by 11.1-25.0%, the number of LUTsdecreased by 44.2-52.2% and the maximum clock frequency increased by 9.3-41.7%. With this technique, we successfully implemented a required FFT on an available FPGA, since the excessive number of LUTs was the bottleneck of the binary FFT.

    DOI: 10.1109/ISMVL.2015.41

    Research data storage URL: http://dblp.uni-trier.de/db/conf/ismvl/ismvl2015.html#conf/ismvl/NakaharaSNI15

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  5. An AWF Digital Spectrometer for a Radio Telescope

    NAKAHARA Hiroki, NAKANISHI Hiroyuki, IWAI Kazumasa

    Technical report of IEICE. VLD   Vol. 114 ( 426 ) page: 67 - 72   2015.1

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    Language:Japanese   Publisher:The Institute of Electronics, Information and Communication Engineers  

    A radio telescope analyzes radio frequency (RF) received from celestial objects. It consists of an antenna, a receiver, and a spectrometer. The spectrometer converts the time domain into the frequency domain by a FFT operation. In the spectrometer, first, it multiples the window coefficient to the received signal. Second, it applies the FFT operation. Third, it converts to the absolute of a complex number. Finally, to reduce the noise, it accumulates obtained power spectrum. We call this a WFA spectrometer. Since an AD converter is faster than the FPGA, a parallel FFT computation is desired. However, since the amount of hardware for the FFT becomes bottleneck, the conventional WFA does not realized the high-performance analysis. This paper proposes an AWF spectrometer which replaces the order of operations. Since the AWF spectrometer reduces the parallelism of the FFT, it is smaller than the conventional WFA spectrometer. Also, the paper proposes a off-chip memory realization which is highly efficient use of the FPGA. Experimental results show that the proposed AWF spectrometer outperforms conventional spectrometers.

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  6. An AWF Digital Spectrometer for a Radio Telescope Reviewed

    Hiroki Nakahara, Hiroyuki Nakanishi, Kazumasa Iwai

    2014 INTERNATIONAL CONFERENCE ON RECONFIGURABLE COMPUTING AND FPGAS (RECONFIG)     2014

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    Language:English   Publisher:IEEE  

    A radio telescope analyzes radio frequency (RF) signal from celestial objects. It consists of an antenna, a receiver, and a spectrometer. The spectrometer converts signal in the time domain into one in the frequency domain by an FFT operation. In the conventional spectrometer, first, it multiples the window coefficient by the received signal. Second, it performs the FFT operation. Third, it converts the signal into the magnitude of the complex number. Finally, to reduce the noise, it accumulates obtained power spectrum. We call this a WFA spectrometer. Since the analog-to-digital converter (ADC) is faster than an FPGA, a parallel FFT computation is desired. However, since the number of on-chip memories for the FFT becomes the bottleneck, the conventional WFA spectrometer could not realize the wide-band and high-resolution. This paper proposes an AWF spectrometer which replaces the order of operations. Since the AWF spectrometer reduces the parallelism of the FFT, it is smaller than the conventional WFA spectrometer. Also, the AWF spectrometer can use a sequential FFT rather than the parallel one. It can be realized by an off-chip memory. Thus, it reduces the number of on-chip memories. Experimental results show that the proposed AWF spectrometer outperforms conventional WFA spectrometers.

    DOI: 10.1109/ReConFig.2014.7032503

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  7. A High-Speed FFT for a Solar Radio Burst Observation On a Radio Telescope

    NAKAHARA Hiroki, CHISHIKI Yohei, IWAI Kazumasa, NAKANISHI Hiroyuki

    IEICE technical report   Vol. 113 ( 325 ) page: 1 - 6   2013.11

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    Language:Japanese   Publisher:The Institute of Electronics, Information and Communication Engineers  

    A radio telescope analyzes radio frequency (RF) received from celestial objects. It consists of an antenna, a receiver, and a spectrometer. The spectrometer converts the time domain into the frequency domain by a FFT operation. A solar radio burst observation requires a high-speed FFT. This paper proposes the high-speed FFT based on Six-Step FFT algorithm. We implement P parallel FFT based on Six-Step FFT algorithm on the Xilinx Virtex 7 VC707 evaluation board. Experimental results shows that the proposed parallel FFT outperforms conventional FFTs.

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  8. New Solar Radio Astronomy by AMATERAS

      Vol. 106 ( 11 ) page: 725 - 732   2013.11

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    CiNii Books

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  9. A HIGH-SPEED FFT BASED ON A SIX-STEP ALGORITHM: APPLIED TO A RADIO TELESCOPE FOR A SOLAR RADIO BURST Reviewed

    Hiroki Nakahara, Kazumasa Iwai, Hiroyuki Nakanishi

    PROCEEDINGS OF THE 2013 INTERNATIONAL CONFERENCE ON FIELD-PROGRAMMABLE TECHNOLOGY (FPT)     page: 430 - 433   2013

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    Language:English   Publisher:IEEE  

    A radio telescope analyzes the radio frequency (RF) received from celestial objects. It consists of an antenna, a receiver, and a spectrometer. The spectrometer converts the time domain into the frequency domain with an FFT operation. A solar radio burst observation requires a high-speed FFT. This paper proposes a P parallel N point FFT for fixed point data based on a six-step algorithm. We analyze the hardware resources for the P parallel N point FFT. We implemented 32 parallel N point FFT circuits on a Xilinx Virtex 7 VC707 board. Comparison with the existing FFT implementations shows that the proposed one is 4.52-22.64 times faster.

    DOI: 10.1109/FPT.2013.6718406

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  10. Survey of Accelerated Particles in a Solar Active Region Using Hinode/XRT and Ground-Based Type-I Radio Burst Observations

    Kazumasa Iwai, Hiroaki Misawa, Fuminori Tsuchiya, Akira Morioka, Satoshi Masuda, Yoshizumi Miyoshi

    HINODE-3: THE 3RD HINODE SCIENCE MEETING   Vol. 454   page: 249 - 252   2012

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    Language:English   Publisher:ASTRONOMICAL SOC PACIFIC  

    The relationships between solar radio type-I bursts and soft X-ray activities were investigated using Hinode/XRT and a ground-based radio telescope belonging to Tohoku University. Although a type-I burst is thought to be generated by high energy non-thermal electrons in the solar corona, the counterpart of this radio burst in X-rays or EUV have yet to be identified. In this study, we found some small scale soft X-ray activities on the XRT images around the onset time of the type-I burst when 10 percent of the soft X-ray flux enhancement around the onset time of the radio burst is defined as a burst-related activity. However, the causal relationship between the observed soft X-ray activities and the onset of the type-I burst are unclear, and more simultaneous observations of radio bursts and X-rays are needed to investigate the coronal counterpart of the type-I burst.

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Research Project for Joint Research, Competitive Funding, etc. 1

  1. Studies on solar storms by developing multi directional radio observation instruments

    2020.10 - 2022.3

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\4000000 ( Direct Cost: \4000000 )

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KAKENHI (Grants-in-Aid for Scientific Research) 8

  1. Challenge to lunar weather forecast by space weather radar and data assimilation simulation

    Grant number:22K18869  2022.6 - 2025.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)  Grant-in-Aid for Challenging Research (Exploratory)

    Kazumasa Iwai

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    Authorship:Principal investigator 

    Grant amount:\6500000 ( Direct Cost: \5000000 、 Indirect Cost:\1500000 )

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  2. 先端のデジタル信号処理を用いた電波観測による太陽嵐3次元構造の解明

    Grant number:21H04517  2021.4 - 2025.3

    日本学術振興会  科学研究費助成事業 基盤研究(A)  基盤研究(A)

    岩井一正

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  3. Forecasting of space disasters using advanced ICT: Challenge to the speace meteorological radar

    Grant number:19K22028  2019.6

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)  Grant-in-Aid for Challenging Research (Exploratory)

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\6370000 ( Direct Cost: \4900000 、 Indirect Cost:\1470000 )

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  4. Investigation of solar storm propagation processes by development of next generation phased array radio telescope

    Grant number:18H01266  2018.4 - 2021.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\17420000 ( Direct Cost: \13400000 、 Indirect Cost:\4020000 )

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  5. Construction of data-assimilation type solar storm arrival prediction model using radio observations

    Grant number:18H04442  2018.4 - 2020.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

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  6. Study of fine spectral structures of solar radio burst by developing a super high-speed digital spectrometer

    Grant number:16K17813  2016.4 - 2019.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)  Grant-in-Aid for Young Scientists (B)

    Iwai Kazumasa

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

    We have developed a digital fast Fourier transform spectrometer made of an analog-to-digital converter (ADC) and a field-programmable gate array (FPGA). High time and spectral resolutions, highly stable spectroscopy, and a wide dynamic range of the spectrometers were demonstrated in a series of laboratory experiments. The developed digital spectrometers were installed in the solar radio telescope of NICT. We detected many fine spectral structures of solar radio bursts from the test observations. These results are summarized in a paper published by the peer-refereed journal.

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  7. 電波観測を用いたリアルタイム宇宙天気予報システムの構築

    Grant number:15J09524  2015.4 - 2017.3

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    岩井 一正

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    太陽の大気コロナでは、フレアに代表される爆発現象や、コロナ質量放出(以下CME)と呼ばれるプラズマ雲の放出現象が発生する。その過程では、強い電波放射(太陽電波バースト)が発生する。粒子の伝搬速度よりも電波の伝搬速度は速いため、電波バーストの検出は宇宙天気災害の有効な予報手段となる。
    山川望遠鏡は受け入れ研究機関であるNICTが新たに開発した太陽電波望遠鏡である。観測周波数帯域は70MHz - 9GHzであり、フレアに起因する太陽電波バーストの発生周波数帯域をほぼ全てカバーできる。本望遠鏡にはFPGAを用いた最新鋭のデジタル分光計OCTAD-Sが搭載され、観測する全帯域で8msの時間分解能で連続観測が可能である。本年度はこの新型分光計の性能評価および査読論文への投稿を行った。論文は現在査読中である。論文化と並行して山川望遠鏡を用いた太陽電波バーストの定常観測を行った。その結果、多数の電波バーストの受信に成功した。特に2016年4月18日に発生した太陽フレアに伴う電波バーストは、NICTが毎日行っている宇宙天気予報の直前に発生した。そのため関連する太陽フレアによって発生した高エネルギー粒子の地球への到来を、電波バーストの情報から到来前に予測し、予報発令に反映させることに成功した。この予報成功は本研究の重要な目的の達成を意味する。今後は電波バーストの自動認識システムを付加することで、粒子の到来前予測の例を増やすことが課題である。
    この他、山川望遠鏡と相補的な情報が得られるミリ波・サブミリ波の太陽観測を実現するために野辺山45m望遠鏡による太陽観測実験を行い、高度高度な較正手法を開発した。この技術を応用して日米欧の国際協力で建設された大型ミリ波・サブミリ波電波干渉計ALMAによる太陽観測国際チームに参画し、ALMAを用いた世界初の太陽観測実験を成功させることに大きく貢献した。

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  8. 太陽電波Type-Iに関する粒子加速過程の研究

    Grant number:09J03264  2009 - 2011

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    岩井 一正

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    太陽から最も頻繁に放射される電波バーストの一つにType-Iがある。この現象は他の太陽電波現象に比べて強度の弱い太陽電波現象である。Type-Iはコロナ中で高エネルギーに加速された電子から放射されると考えられているが、その電子を高エネルギーに加速する過程はいまだ明らかになっていない。これら高エネルギー粒子の生成過程は、太陽コロナの物理を議論する上で極めて重要であるとともに、未知の加速課程の発見につながる可能性がある。そこで本研究では微弱な太陽電波バーストType-Iを発生させる高エネルギー電子の加速過程を解明することを目的とし、地上電波観測を中心とした研究活動を行ってきた。その結果、本年度に以下の成果が得られた。
    1:観測システムの連続運用・データアーカイブ化
    本研究では微弱な電波強度で微細なスペクトル構造を伴い放射されるType-Iバーストを効果的に観測するための電波観測装置(IPRT/mmTERAS)を開発した。連続運用フェーズに移行した本年度は、全自動運用システムの開発・観測データのアーカイブ化・データ公開システムの構築と装置論文の執筆を行った。その結果、全自動での運用およびデータアーカイブ化に成功した。また観測データは観測日中にWebから公開することが可能となった。
    2:超微細Type-Iバーストの発見
    Type-Iには継続時間1秒未満の微細なスペクトル構造が多数含まれていることが知られている。本研究ではType-Iの微細なスペクトル構造に注目し、Type-Iの高分解スペクトル観測を行い、そのデータの解析を行った。その結果Type-Iには今まで連続成分とみなされた電波成分にも多量の微細バーストが含まれていることを発見した。加えてType-Iバースト成分の統計的特徴に注目し、電波強度の発生頻度解析を行った。その結果、バースト成分の電波強度は幕状分布し、その指数は-2から-3と通常のType-III電波バーストやフレア現象よりスペクトルが急峻であることが示唆された。

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Teaching Experience (On-campus) 3

  1. 物理学実験

    2019

  2. Space-Earth Radio Science

    2019

  3. 先端物理学特論

    2019

Teaching Experience (Off-campus) 3

  1. 物理学実験

    2019 名古屋大学 理学部)

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  2. Space-Earth Radio Science

    2018 Nagoya University)

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  3. 先端物理学特論

    2017 名古屋大学 理学部)

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