Faculty Profiles - SHIOKAWA, Kazuo

Turbulent microstructures and formation of folds in auroral breakup arc Reviewed Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 ( 4 ) 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We conducted a ground-based optical measurement pointing at local magnetic zenith with a narrow field of view of 9.3 degrees by 9.3 degrees, 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 Alfven 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.

DOI： 10.1029/2010JA016334

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 Reviewed

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 Vol. 5 ( 1 ) page： 82 - 83 2011.4

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

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

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 4 ) 2011.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

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 similar to 300 km and propagated toward the northwest with a phase velocity of similar to 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. Citation: Adachi, T., Y. Otsuka, M. Yamaoka, M. Yamamoto, K. Shiokawa, A. B. Chen, and R.-R. Hsu (2011), First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL, Geophys. Res. Lett., 38, L04101, doi:10.1029/2010GL046268.

DOI： 10.1029/2010GL046268

Periodic black auroral patches at the dawnside dipolarization front during a substorm Reviewed

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 2011.1

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

ULF impulsive magnetic response at mid-latitudes to lightning activity Reviewed Open Access

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

EARTH PLANETS AND SPACE Vol. 63 ( 2 ) page： 119 - 128 2011

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

Induction magnetometer data from the mid-latitude station Moshiri (geomagnetic latitude 35.6 degrees.) 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.

DOI： 10.5047/eps.2010.12.009

Atmospheric wave induced O-2 and OH airglow intensity variations: effect of vertical wavelength and damping Reviewed Open Access

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

ANNALES GEOPHYSICAE Vol. 29 ( 4 ) page： 631 - 637 2011

Motion of polar cap arcs Reviewed Open Access

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

Journal of Geophysical Research Vol. 116 ( 1 ) 2011

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes Reviewed Open Access

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

Journal of Geophysical Research: Space Physics Vol. 116 ( 1 ) 2011

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

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

プラズマバブルに伴う全電子数変化率・ロック損失分布 : ロック損失発生の有無と全電子数変化率の相関 Reviewed

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

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

AERONOMY OF THE EARTH'S ATMOSPHERE AND IONOSPHERE Vol. 2 page： 291 - 299 2011

Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.12

Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan Reviewed Open Access

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

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 115 2010.12

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

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 4 ( 2 ) page： 80 - 81 2010.10

Simultaneous FAST and Double Star TC1 observations of broadband electrons during a storm time substorm Reviewed Open Access

A. Nakajima, K. Shiokawa, K. Seki, R. Nakamura, K. Keika, W. Baumjohann, T. Takada, J. P. McFadden, C. W. Carlson, A. N. Fazakerley, H. Reme, I. Dandouras, R. J. Strangeway, O. Le Contel, N. Cornilleau-Wehrlin, K. H. Yearby

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355-1359 UT, similar to 61 degrees-66 degrees invariant latitudes, similar to 0600 magnetic local time (MLT), and similar to 3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H-bay at similar to 1349 UT at similar to 0600 MLT, indicating that a storm time substorm started just before the appearance of the BBEs. At similar to 1350 UT, a tailward ion flow was observed by DS TC1. Then, DS TC1 observed a local dipolarization and a drastic ion density enhancement at similar to 1351 UT, indicating that particle heating associated with the substorm was occurring in the inner magnetosphere. From similar to 1352 UT, electron fluxes were isotropically enhanced at energies above similar to 0.5 keV as observed by DS TC1. On the other hand, the pitch angle distribution of BBEs at the FAST altitude showed field-aligned lower-energy electrons below similar to 0.5 keV and isotropic higher-energy electrons above similar to 0.5 keV. From these data, it was inferred that the BBEs might consist of two energy components due to the acceleration or heating of electrons at different altitudes in association with the storm time substorm.

DOI： 10.1029/2009JA014907

プラズマバブルに伴うGPSロック損失・全電子数変化率分布のマルチイベント解析 Reviewed

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 Vol. 4 ( 1 ) page： 58 - 59 2010.4

Rayleigh-Taylor type instability in auroral patches Reviewed

K. Shiokawa, A. Nakajima, A. Ieda, K. Sakaguchi, R. Nomura, T. Aslaksen, M. Greffen, E. Donovan

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.2

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Based on observations by a high-resolution narrow field-of-view CCD camera, we found small-scale (5-25 km) finger-like structures at the western boundary of auroral patches in images obtained at Gillam (geomagnetic latitude: 65.5 degrees N), Canada, in January 2008. Since shear motion was not observed along the boundary of the patches, we suggest that these structures are formed by macroscopic Rayleigh-Taylor type plasma instability arising in the magnetospheric equatorial plane from the force balancing of the (eastward) magnetic tension force and the (westward) pressure gradient force.

DOI： 10.1029/2009JA014273

A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed Open Access

Balan N., Shiokawa K., Otsuka Y., Kikuchi T., Lekshmi D. Vijaya, Kawamura S., Yamamoto M., Bailey G. J.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.2

Reorganization of polar cap patches through shears in the background plasma convection Reviewed

Hosokawa K., St-Maurice J. -P., Sofko G. J., Shiokawa K., Otsuka Y., Ogawa T.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.1

The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations Reviewed Open Access

K. Shiokawa, R. Nomura, K. Sakaguchi, Y. Otsuka, Y. Hamaguchi, M. Satoh, Y. Katoh, Y. Yamamoto, B. M. Shevtsov, S. Smirnov, I. Poddelsky, M. Connors

EARTH PLANETS AND SPACE Vol. 62 ( 6 ) page： 517 - 524 2010

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

The Solar-Terrestrial Environment Laboratory (STEL) induction magnetometer network has been developed to investigate the propagation characteristics of high-frequency geomagnetic pulsations in the Pc1 frequency range (0.2-5 Hz). Five induction magnetometers were installed in the period 2005-2008 at Athabasca in Canada, Magadan and Paratunka in Far East Russia, and Moshiri and Sata in Japan. The sensitivity of these magnetometers is between 0.3 and 13 V/nT at turnover frequencies of 1.7-5.5 Hz. GPS time pulses are used for accurate triggering of the 64-Hz data sampling. We show examples of PiB/Pc1 magnetic pulsations observed at these five stations, as well as the harmonic structure of ionospheric Alfven resonators observed at Moshiri. We found that the Pc1 packets are slightly modulated as they propagate from high to low latitudes in the ionospheric duct. These network observations are expected to contribute to our understanding of Pc1-range magnetic pulsations and their interaction with relativistic electrons by combining the obtained results with future satellite missions that observe radiation belt particles.

DOI： 10.5047/eps.2010.05.003