研究者詳細 - 塩川　和夫

論文 - 塩川　和夫

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VHF radar observations of post-midnight f-region field-aligned irregularities over indonesia during solar minimum 査読有り

Otsuka Y., Shiokawa K., Nishioka M., Effendy

Indian Journal of Radio and Space Physics 41 巻 ( 2 ) 頁： 199 - 207 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Indian Journal of Radio and Space Physics

A VHF backscatter radar with operating frequency 30.8 MHz has been operated at Kototabang (0.20°S, 100.32°E; dip latitude 10.4°S), Indonesia since February 2006. The F-region field-aligned irregularities (FAIs) observed by this radar from February 2006 to December 2010 during a solar minimum period have been analyzed and found that FAIs appeared frequently at the post-midnight sector between May and August every year from 2006 to 2010. Five-beam measurements by the radar revealed zonal propagation of the F-region FAIs. The present paper reports, for the first time, statistics of the zonal propagation velocity of the post-midnight FAIs. Between May and August, 46% (14%) of the post-midnight FAIs propagated westward (eastward), and zonal propagation was not discernible for 40% of the post-midnight FAIs. Average velocity was approximately 50 m s-1 westward. The post-midnight FAIs were likely associated with either plasma bubbles or medium-scale traveling ionospheric disturbances (MSTIDs).

Scopus

High-latitude GPS TEC changes associated with a sudden magnetospheric compression 査読有り

Jayachandran P. T., Watson C., Rae I. J., MacDougall J. W., Danskin D. W., Chadwick R., Kelly T. D., Prikryl P., Meziane K., Shiokawa K.

GEOPHYSICAL RESEARCH LETTERS 38 巻 ( 23 ) 2011年12月

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

Using ionospheric total electron content (TEC) measured by Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN) we provide clear evidence for a systematic and propagating temporary TEC enhancement produced by compression of the magnetosphere due to a sudden increase in solar wind dynamic pressure. The magnetospheric compression is evident in THEMIS/GOES satellite data. Application of a GPS triangulation technique revealed that the TEC changes propagated with a speed of 3-6 km/s in the antisunward direction near noon and ∼8 km/s in the sunward direction in the pre-noon lower latitude sector. Characteristics of these TEC changes along with riometer absorption measurements seems to indicate that the TEC change is due to electron density enhancement in the F region and is possibly due to particle precipitation associated with sudden magnetospheric compression. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011GL050041

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Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging 査読有り

Lynn K. J. W., Otsuka Y., Shiokawa K.

GEOPHYSICAL RESEARCH LETTERS 38 巻 ( 23 ) 2011年12月

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

Airglow observations of ionospheric electron density depletions made at Darwin, Australia have demonstrated that the tree-like structure of bubbles developed at the magnetic equator are mapped along magnetic field lines with considerable accuracy to the base of the ionosphere at higher latitudes. Ionosonde range-time displays made at Darwin and other equatorial sites in the Australian region show characteristic approaching and receding echoes which converge on a typical spread-F event. These off-angle echoes have often been referred to in the literature as satellite traces and associated with spread F with little recognition of their true significance. All four optical depletions previously reported in the literature as being seen at Darwin are found in this paper to be accompanied by such typical off-angle/spread F events. The zonal drift velocity of the moving reflectors can be measured from the speed at which such echoes approach and recede. Since digital ionosondes in equatorial sites have existed for many years, existing ionogram data, when suitably processed into range-time displays, may allow the occurrence of such events over several sunspot cycles to be found. A question remains as to whether all or only some of such equatorial range-time events correspond to electron density depletions. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011GL049856

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A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) 査読有り

Lee S., Shiokawa K., McFadden J. P., Nishimura Y.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年12月

Long-term variations in tweek reflection height in the D and lower E regions of the ionosphere 査読有り Open Access

Ohya, H; Shiokawa, K; Miyoshi, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 ( 10 ) 2011年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

We investigated, for the first time, long-term (1976-2010) variations in reflection heights of tweek atmospherics based on very low frequency (VLF) observations at Kagoshima, Japan. The results revealed the effects of the solar cycle on the nighttime lower ionosphere at low to middle latitudes. The tweek reflection heights on geomagnetically quiet days were analyzed every month over three solar cycles by using an automated spectral fitting procedure to estimate the cutoff frequency. The average and standard deviation of the reflection height were 95.9 km and ±3.1 km, respectively. Typical periods of time variation for the reflection height were 13.3, 3.2, 1.3, 1.0, 0.6, and 0.5 years. The variations in tweek reflection heights did not show simple anticorrelation with solar activity. The correlation coefficient between tweek reflection height and sunspot number was 0.03 throughout the three solar cycles. Hilbert-Huang transform analysis successfully indicated the presence of 0.5-1.5 year and ∼10 year variations as intrinsic mode functions (IMF). The decomposed IMF with the ∼10 year variation had a positive correlation with sunspot numbers and a negative correlation with galactic cosmic rays (GCRs). We hypothesize that these variations in tweek reflection heights could be caused by coupling of several ionization effects at the D and lower E regions, effects such as geocorona, GCRs, particle precipitation, and variations in neutral density in the lower thermosphere. Among these processes, the geocorona and particle precipitation could show negative correlation, while the GCRs and neutral density could show positive correlation with solar activities. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011JA016800

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ジオスペース探査ERG計画(Technical Session,ICSANE 2011(International Conference on Space, Aeronautical and Navigational Electronics 2011))

小野高幸, 浅村和史, 三好由純, 高島健, 平原聖文, 小原隆博, 笠羽康正, 熊本篤志, 松岡彩子, 小嶋浩嗣, 塩川和夫, 関華奈子, 藤本正樹, 長妻努

電子情報通信学会技術研究報告. SANE, 宇宙・航行エレクトロニクス 111 巻 ( 239 ) 頁： 57 - 61 2011年10月

An empirical model of the quiet daily geomagnetic field variation 査読有り

Y. Yamazaki, K. Yumoto, M. G. Cardinal, B. J. Fraser, P. Hattori, Y. Kakinami, J. Y. Liu, K. J. W. Lynn, R. Marshall, D. McNamara, T. Nagatsuma, V. M. Nikiforov, R. E. Otadoy, M. Ruhimat, B. M. Shevtsov, K. Shiokawa, S. Abe, T. Uozumi, A. Yoshikawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年10月

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

An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp <= 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

DOI： 10.1029/2011JA016487

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Ground-based multispectral high-speed imaging of flickering aurora 査読有り

Kataoka Ryuho, Miyoshi Yoshizumi, Sakanoi Takeshi, Yaegashi Ayumi, Ebihara Yusuke, Shiokawa Kazuo

GEOPHYSICAL RESEARCH LETTERS 38 巻 ( 14 ) 2011年7月

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

It has been suggested that dispersive Alfven waves (DAWs) are capable of accelerating electrons via Landau resonance, and the interference of DAWs plays an essential role to create flickering auroral patterns. Here we show evidence that the leading front of a typical interference pattern is more energetic than the trailing part, based on ground-based high-speed imaging observations at wavelengths of 670.5 nm and 844.6 nm, which are sensitive to relatively hard and soft electrons, respectively. The fine spatial resolution of 9.5 deg field-of-view at magnetic zenith and the 100 Hz sampling rate of electron multiplying charge-coupled device (EMCCD) enabled us to resolve the spatiotemporal variation of the flickering aurora. It is found that there is only 10 ms time delay with 0.5 km spatial shift on average in the obtained flickering patterns at two wavelengths. The time delay and spatial shift can be comprehensively explained by the traveling inhomogeneous interference pattern of DAWs, probably associated with the Landau damping and/or time-of-flight effect, which is only detectable using the highest resolved temporal and spatial observations of flickering aurora. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011GL048317

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Decay of polar cap patch 査読有り

Hosokawa, K; Moen, JI; Shiokawa, K; Otsuka, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 ( 5 ) 2011年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

We report an event in which a polar cap patch was detected with an all-sky imager (ASI) at Resolute Bay, Canada (74.73° N, 265.07° E; AACGM latitude 82.9°), on the nightside. The patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the ASI for more than 1 h. When the patch stagnated, its luminosity decreased gradually, which allows us to investigate how the patch plasma decayed in a quantitative manner. The decay of the patch can be quantitatively explained by the loss through recombinations of O+ with ambient N2 and O2 molecules, if we assume the altitude of the optical patch to be around 295 km. The derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the MSIS-E90 and IRI-2007 models, indicating that climatological models such as IRI are not suitable for describing the actual density profile of patches. This is probably because the loss process was much faster in the lower-altitude part of the patch; thus, the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the F region. This suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap. Such information is important when we compare the optical data with other instruments such as coherent radars and GPS scintillation measurements by mapping the all-sky image on the geographic coordinate system with an assumption of the patch emission altitude. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA016297

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Turbulent microstructures and formation of folds in auroral breakup arc 査読有り Open Access

Kataoka, R; Miyoshi, Y; Sakanoi, T; Yaegashi, A; Shiokawa, K; Ebihara, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 ( 4 ) 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

We conducted a ground-based optical measurement pointing at local magnetic zenith with a narrow field of view of 9.3 by 9.3, using a high-speed electron multiplier charge-coupled device camera at Poker Flat Research Range. We show evidence that auroral folds were periodically formed in a breakup arc and the luminosity is exponentially increased for about 10 s before an auroral breakup onset. The evolution of turbulent microstructures and the formation of folds may be interpreted by the nonlinear evolution of inertial Alfvén wave (IAW) turbulence in the thin current sheet. On the basis of these optical observations, we discuss a possible role of the ionosphere for modulating the triggering process of the onset via the self-organization of the IAW turbulence associated with Kelvin-Helmholtz and tearing instabilities of the thin current sheet. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA016334

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GEONETにおけるプラズマバブルに伴う全電子数変化率とロック損失との相関査読有り

菊地隼人, 中田裕之, 津川卓也, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 = / Society of Atmospheric Electricity of Japan 5 巻 ( 1 ) 頁： 82 - 83 2011年4月

First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL 査読有り

Adachi Toru, Otsuka Yuichi, Yamaoka Masashi, Yamamoto Mamoru, Shiokawa Kazuo, Chen Alfred B., Hsu Rue-Ron

GEOPHYSICAL RESEARCH LETTERS 38 巻 ( 4 ) 2011年2月

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

On the night of May 16, 2007, a satellite limb imager of FORMOSAT-2/ISUAL observed wave-like structures of the 630-nm airglow simultaneously with an all-sky imager deployed at Darwin in Australia. The height of the airglow layer was estimated as 220 km, and the structures were aligned in the northeast-southwest orientation with a wavelength of ∼300 km and propagated toward the northwest with a phase velocity of ∼100 m s-1, showing typical characteristics of the nighttime medium-scale traveling ionospheric disturbances (MSTIDs). We conclude that ISUAL for the first time succeeded in observing the airglow layer altitude and airglow structures modulated by MSTID from space. Such a satellite limb airglow imaging could be a new tool to characterize ionospheric irregularities on a global level. Copyright © 2011 by the American Geophysical Union.

DOI： 10.1029/2010GL046268

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Periodic black auroral patches at the dawnside dipolarization front during a substorm 査読有り

K. Sakaguchi, K. Shiokawa, E. Donovan, A. Nakajima, Y. Hiraki, T. Trondsen, F. Plaschke

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 116 巻 2011年1月

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

Periodic black auroral patches were observed in the Canadian postmidnight sector by ground-based all-sky cameras during an auroral substorm. The aurora consisted of several black patches of similar to 50 km (similar to 1 degrees in longitude) scales that appeared along the equatorward edges of the proton auroras over a 3 h local time segment from Gillam to Sanikiluaq ground stations 15 min after the auroral intensification occurred in Alaska. To the best of our knowledge, this type of black auroras has never been reported before, although the surrounding luminous auroras evolve into the well-known torch structures later. In situ observations by the THEMIS satellites, three of which were close to being magnetically conjugate in the plasma sheet, as well as ground-based proton auroral observations, show that a dipolarization front and associated dawnward ion flows propagated eastward at poleward of the black patches coinciding with their appearance. The flow motions of auroras observed poleward of the black patches are possibly generated by decelerations of dawnward ion flow because of the consistency of both durations and positions. We speculate, based on manifestations of high-pressure regions in dipolarized flux tubes, the pressure-driven interchange instability formed a beading shape (periodic black patches) of field-aligned currents. The black auroral patches developed into torch structures after the flow disappearance, indicating the dawnward flows might stabilize and limit the instability within a narrow L shell where the pressure gradient is directed Earthward and flows cannot enter. We conclude that the periodic black patches arise as a consequence of a relaxation process of enhanced plasma pressure near the inner boundary of the plasma sheet during a substorm.

DOI： 10.1029/2010JA015957

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ULF impulsive magnetic response at mid-latitudes to lightning activity 査読有り

Schekotov A., Pilipenko V., Shiokawa K., Fedorov E.

EARTH PLANETS AND SPACE 63 巻 ( 2 ) 頁： 119 - 128 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

Induction magnetometer data from the mid-latitude station Moshiri (geomagnetic latitude 35.6°) has been examined in search of a transient ULF response to the regional lightning activity. For many events, besides the main impulse produced by the lightning discharge, a secondary impulse delayed about 1 sec was observed. These secondary echo-impulses are probably caused by the partial reflection of wave energy of the initial lightning pulse from the upper boundary of the ionospheric Alfven resonator in the topside ionosphere. The modeling with artificial signals has shown that a multi-band spectral resonant structure (SRS) can be formed owing to the occurrence of paired pulses in analyzed time series. The statistical superposed epoch method indeed has revealed a dominance of two-pulse structure in the magnetic field background during the periods of the SRS occurrence. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

DOI： 10.5047/eps.2010.12.009

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Atmospheric wave induced O2 and OH airglow intensity variations: effect of vertical wavelength and damping 査読有り

Takahashi H., Onohara A., Shiokawa K., Vargas F., Gobbi D.

ANNALES GEOPHYSICAE 29 巻 ( 4 ) 頁： 631 - 637 2011年

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

From nocturnal variations of the airglow O2 (0-1) and OH Meinel (6-2) band emission intensity and the rotational temperature, gravity waves and the damping effect in the MLT region were investigated. The data set was obtained from photometer measurements at Rikubetsu (43.5° N, 143.8° E), Japan, from March 2004 to August 2005. The ratio of the amplitude of oscillation and their phase difference between the two emissions were calculated when simultaneous periodic variations were observed. The ratio showed a linear correlation with the phase difference. The vertical wavelength and damping rate were estimated by using a model calculation carried out by previous works. The results show that the wave damping is significant when the vertical wavelength is shorter than 30-40 km. Krassovsky's parameter η, which represents a ratio between the emission intensity and temperature oscillations, was also calculated. The results show that the η also depends on the damping effect. © Author(s) 2011.

DOI： 10.5194/angeo-29-631-2011

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Motion of polar cap arcs 査読有り Open Access

Hosokawa K., Moen J.I., Shiokawa K., Otsuka Y.

Journal of Geophysical Research: Space Physics 116 巻 ( 1 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

A statistics of motion of polar cap arcs is conducted by using 5 years of optical data from an all-sky imager at Resolute Bay, Canada (74.73°N, 265.07°E). We identified 743 arcs by using an automated arc detection algorithm and statistically examined their moving velocities as estimated by the method of Hosokawa et al. (2006). The number of the arcs studied is about 5 times larger than that in the previous statistics of polar cap arcs by Valladares et al. (1994); thus, we could expect to obtain more statistically significant results. Polar cap arcs are found to fall into two distinct categories: the By-dependent and By-independent arcs. The motion of the former arcs follows the rule reported by Valladares et al. (1994), who showed that stable polar cap arcs move in the direction of the interplanetary magnetic field (IMF) By. About two thirds of the arcs during northward IMF conditions belong to this category. The latter arcs always move poleward irrespective of the sign of the IMF By, which possibly correspond to the poleward moving arcs in the morning side reported by Shiokawa et al. (1997). At least one third of the arcs belong to this category. The By-dependent arcs tend to move faster when the magnitude of the IMF By is larger, suggesting that the transport of open flux by lobe reconnection from one polar cap compartment to the other controls their motion. In contrast, the speed of the By-independent arcs does not correlate with the magnitude of the By. The motions of both the B y-dependent and By-independent arcs are most probably caused by the magnetospheric convection. Convection in the region of B y-dependent arcs is affected by the IMF By, which indicates that their sources may be on open field lines or in the closed magnetosphere adjacent to the open-closed boundary, whereas B y-independent arcs seem to be well on closed field lines. Hence, the magnetospheric source of the two types of arc may be different. This implies that the mechanisms causing the motion and generation of arcs could be different between the two types of polar cap arc. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA015906

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Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes 査読有り

Nomura R., Shiokawa K., Pilipenko V., Shevtsov B.

Journal of Geophysical Research: Space Physics 116 巻 ( 1 ) 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

We have investigated Pc1 geomagnetic pulsations observed by induction magnetometers at three low-latitude stations (Paratunka (PTK), Moshiri (MSR), and Sata (STA), L=1.2-2.1). A detailed polarization analysis shows that polarization parameters (angle of polarization ellipse orientation, ψ, and polarization sense, ε) of individual Pc1 bands depend on frequency at all three stations. The dependence of ψ on frequency was seen in ∼70% of the 93 Pc1 events observed at MSR (L=1.5) from 14 July 2007 to 13 July 2009. The maxima of seasonal and diurnal variations of the occurrence rate were in winter and during the nighttime, as reported previously, indicating that the transmission of observed Pc1 pulsations to lower latitudes is controlled by the density of the F layer plasma. These facts suggest that spatially distributed Pc1 waves with varying frequencies depending on longitude or latitude at high latitudes propagated in the ionospheric duct to cause the frequency dependence of polarization parameters at low latitudes. We also suggest that the Pc1 pearl structure with a repetition period of ∼5-30 s observed at low latitudes is a beat of high-latitude waves with slightly different frequencies. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA015684

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Statistical Study of Medium-Scale Traveling Ionospheric Disturbances Observed with a GPS Receiver Network in Japan 査読有り

Otsuka Y., Kotake N., Shiokawa K., Ogawa T., Tsugawa T., Saito A.

AERONOMY OF THE EARTH'S ATMOSPHERE AND IONOSPHERE 2 巻頁： 291 - 299 2011年

Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm 査読有り

Hosokawa K., Tsugawa T., Shiokawa K., Otsuka Y., Nishitani N., Ogawa T., Hairston M. R.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 115 巻 2010年12月

Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan 査読有り

Suzuki S., Nakamura T., Ejiri M. K., Tsutsumi M., Shiokawa K., Kawahara T. D.

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 115 巻 2010年12月

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