Faculty Profiles - SHIOKAWA, Kazuo

Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil Reviewed

H. Takahashi, S. Costa, Y. Otsuka, K. Shiokawa, J. F. G. Monico, E. Paula, P. Nogueira, C. M. Denardini, F. Becker-Guedes, C. M. Wrasse, A. S. Ivo, V. C. F. Gomes, W. Gargarela, N. Sant'Anna, R. Gatto

ADVANCES IN SPACE RESEARCH Vol. 54 ( 3 ) page： 385 - 394 2014.8

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

The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 mm and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (ETA) and post-sunset plasma enhancement (PS-ETA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in ETA and PS-ETA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2014.01.032

Day-night coupling by a localized flow channel visualized by polar cap patch propagation Reviewed Open Access

Y. Nishimura, L. R. Lyons, Y. Zou, K. Oksavik, J. I. Moen, L. B. Clausen, E. F. Donovan, V. Angelopoulos, K. Shiokawa, J. M. Ruohoniemi, N. Nishitani, K. A. McWilliams, M. Lester

GEOPHYSICAL RESEARCH LETTERS Vol. 41 ( 11 ) page： 3701 - 3709 2014.6

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

We present unique coordinated observations of the dayside auroral oval, polar cap, and nightside auroral oval by three all-sky imagers, two Super Dual Auroral Radar Network (SuperDARN) radars, and Defense Meteorological Satellite Program (DMSP)-17. This data set revealed that a dayside poleward moving auroral form (PMAF) evolved into a polar cap airglow patch that propagated across the polar cap and then nightside poleward boundary intensifications (PBIs). SuperDARN observations detected fast antisunward flows associated with the PMAF, and the DMSP satellite, whose conjunction occurred within a few minutes after the PMAF initiation, measured enhanced low-latitude boundary layer precipitation and enhanced plasma density with a strong antisunward flow burst. The polar cap patch was spatially and temporally coincident with a localized antisunward flow channel. The propagation across the polar cap and the subsequent PBIs suggests that the flow channel originated from dayside reconnection and then reached the nightside open-closed boundary, triggering localized nightside reconnection and flow bursts within the plasma sheet.

DOI： 10.1002/2014GL060301

Height-dependent ionospheric variations in the vicinity of nightside poleward expanding aurora after substorm onset Reviewed Open Access

S. Oyama, Y. Miyoshi, K. Shiokawa, J. Kurihara, T. T. Tsuda, B. J. Watkins

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 5 ) page： 4146 - 4156 2014.5

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

High-latitude ionospheric variations at times near auroral substorms exhibit large temporal variations in both vertical and horizontal extents. Statistical analysis was made of data from the European Incoherent Scatter UHF radar at TromsO, Norway, and International Monitor for Auroral Geomagnetic Effects magnetometer for finding common features in electron density, ion and electron temperatures and relating these to currents and associated heating. This paper particularly focused on the height dependencies. Results show clear evidences of large electric field with corresponding frictional heating and Pedersen currents located just outside the front of the poleward expanding aurora, which typically appeared at the eastside of westward traveling surge. At the beginning of the substorm recovery phase, the ionospheric density had a large peak in the E region and a smaller peak in the F region. This structure was named as C form in this paper based on its shape in the altitude-time plot. The lower altitude density maximum is associated with hard auroral electron precipitation probably during pulsating aurora. We attribute the upper F region density maximum to local ionization by lower energy particle precipitation and/or long-lived plasma that is convected horizontally into the overhead measurement volume from the dayside hemisphere.

DOI： 10.1002/2013JA019704

Pi2 pulsation simultaneously observed in the E and F region ionosphere with the SuperDARN Hokkaido radar Reviewed Open Access

M. Teramoto, N. Nishitani, V. Pilipenko, T. Ogawa, K. Shiokawa, T. Nagatsuma, A. Yoshikawa, D. Baishev, K. T. Murata

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 5 ) page： 3444 - 3462 2014.5

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

We investigated Pi2 pulsations in the nightside ionosphere that began at 14:15 UT (2315 LT) on 11 July 2010, and they were observed with high-temporal (8s) resolution by beam 4 of the Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar. These pulsations were simultaneously observed in both the ground/sea scatter echoes reflected from the F region height and in ionospheric echoes from field-aligned irregularities in the sporadic Es region. They had the same period of 110s and approximately no phase lag. From the radar observations and the International Geomagnetic Reference Field model, the amplitude of the eastward (EEW) component of the electric field of the Pi2 pulsations in the ionosphere was estimated similar to 8.0mV/m in the F region and similar to 2.0mV/m in the E region. Corresponding Pi2 pulsations appeared dominantly in the horizontal northward magnetic field component (H) at nearby ground stations, Moshiri (MSR), St. Paratunka (PTK), and Stecolny (STC), with amplitudes ranging from 6 nT (MSR) to 10 nT (STC). At the dominant frequency of 8.8 mHz, the coherences between H and EEW were high (>0.9), the cross phases of EEW relative to H were -56 degrees and -45 degrees, and the amplitude ratios were 2.7x105m/s and 8.4x105m/s, in the E and F regions, respectively. Based on a comparison of these results with theoretical predictions, we suggest that the concept of a pure cavity mode is not sufficient to explain the combined observations for midlatitude Pi2 waves and that the contribution of an Alfven waves must be taken in account.

DOI： 10.1002/2012JA018585

Global imaging of polar cap patches with dual airglow imagers Reviewed Open Access

K. Hosokawa, S. Taguchi, K. Shiokawa, Y. Otsuka, Y. Ogawa, M. Nicolls

GEOPHYSICAL RESEARCH LETTERS Vol. 41 ( 1 ) page： 1 - 6 2014.1

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

During a 2 h interval from 2240 to 2440 UT on 12 November 2012, regions of increased 630.0 nm airglow emissions were simultaneously detected by dual all-sky imagers in the polar cap, one at Longyearbyen, Norway (78.1 degrees N, 15.5 degrees E) and the other at Resolute Bay, Canada (74.7 degrees N, 265.1 degrees E). The Resolute Bay incoherent scatter radar observed clear enhancements of the F region electron density up to 10(12) m(-3) within these airglow structures which indicates that these are optical manifestations of polar cap patches propagating across the polar cap. During this interval of simultaneous airglow imaging, the nightside/dawnside (dayside/duskside) half of the patches was captured by the imager at Longyearbyen (Resolute Bay). This unique situation enabled us to estimate the dawn-dusk extent of the patches to be around 1500 km, which was at least 60-70% of the width of the antisunward plasma stream seen in the Super Dual Auroral Radar Network convection maps. In contrast to the large extent in the dawn-dusk direction, the noon-midnight thickness of each patch was less than 500 km. These observations demonstrate that there exists a class of patches showing cigar-shaped structures. Such patches could be produced in a wide range of local time on the dayside nearly simultaneously and spread across many hours of local time soon after their generation.

DOI： 10.1002/2013GL058748

Deducing Locations and Electrical properties of Lightning Discharges by ELF Network Observations in Japan Reviewed

Yasuhide Hobara, Masashi Hayaka, Kazuo Shiokawa

2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS) page： . 2014

Latitudinal variation of stochastic properties of the geomagnetic field Reviewed Open Access

Wanliss J. A., Shiokawa K., Yumoto K.

NONLINEAR PROCESSES IN GEOPHYSICS Vol. 21 ( 2 ) page： 347-356 2014

Ground-Based Observations of Hiss-Like Emissions Changed from Chorus Emissions and Related Pulsating Aurora Reviewed

Ozaki M., Sawai K., Yagitani S., Shiokawa K., Miyoshi Y., Kataoka R., Ieda A., Ebihara Y., Katoh Y.

2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS) 2014

Deducing locations and charge moment changes of lightning discharges by ELF network observations in Japan Reviewed Open Access

Hobara Y., Inoue T., Hayakawa M., Shiokawa K.

International Conference on Atmospheric Electricity Icae 2014 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：International Conference on Atmospheric Electricity Icae 2014

Recent observations of electromagnetic radiations from lightning in the ELF frequency range so-called ELF transients are recognized as a powerful tool not only to deduce the global lightning distribution but also to obtain one of the most important properties of lightning discharges such as charge moment changes (CMCs). In this paper we demonstrate the spatio-temporal distributions of lightning discharges together with CMCs around Japan by using our newly developed domestic ELF observation network. This is the first time to obtain such type of distribution by using only ELF observations in the spatial scale of Japan (a few thousands km). We found that the obtained lightning source distributions both over the Pacific Ocean and the Sea of Japan are originated from the thunderstorm active regions confirmed by other measurements such as WWLLN. Statistical properties of the charge moment changes indicate that both number and CMC of positive CGs are superior to those of negative CGs. Moreover, considerably large CMC with both polarities are identified for the CGs over the Pacific Ocean as well as those with positive polarity over the Sea of Japan. Furthermore, we are going to present updated our lightning measurement network in Japan.

DOI： 10.1541/ieejpes.133.994

Deducing Locations and Charge Moment Changes of Lightning Discharges by ELF Network Observations in Japan Open Access

Hobara Yasuhide, Inoue Takahiro, Hayakawa Masashi, Shiokawa Kazuo

IEEJ Transactions on Power and Energy Vol. 133 ( 12 ) page： 994 - 1000 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

The electromagnetic radiations from lightning discharges have been intensively studied for a long time in different frequency ranges. Recent observations of electromagnetic radiations from lightning in the ELF (extremely low frequency) frequency range so-called ELF transients are recognized as a powerful tool to obtain one of the most important properties of lightning discharges; the charge moment changes (<i>Qds</i>). In this paper we demonstrate the spatio-temporal distributions of lightning discharges together with their charge moment change (CMC) around Japan by using our newly developed domestic ELF observation network. This is the first time to obtain such type of distribution by using only ELF observations in the spatial scale of Japan (a few thousands km). We found that the obtained lightning source distributions both over the Pacific Ocean and the Sea of Japan are originated from the thunderstorm active regions confirmed by other measurements such as WWLLN. Statistical properties of the charge moment changes indicate that both number and CMC of positive CGs are superior to those of negative CGs. Moreover considerably large CMC with both polarities are identified for the CGs over the Pacific Ocean as well as those with positive polarity over the Sea of Japan.

DOI： 10.1541/ieejpes.133.994

CiNii Research

イオノゾンデおよびファブリ・ペロー干渉計によって観測された子午面熱圏風の比較 Reviewed Open Access

Nishioka Michi, Maruyama Takashi, Otsuka Yuichi, Tsugawa Takuya, Ishibashi Hiromitsu, Shiokawa Kazuo, Ishii Mamoru

Antarctic record Vol. 57 ( 3 ) page： 357 - 368 2013.11

Language：English Publishing type：Research paper (scientific journal) Publisher：National Institute of Polar Research

電離圏ダイナミクスに大きく寄与する熱圏風についての理解を深めるため,イオノゾンデの磁気共役点観測により推定された南北方向の熱圏風(推定熱圏風)と,ファブリ・ペロー干渉計(FPI)観測により直接測定された南北方向の熱圏風との相関を調べた.推定熱圏風は,磁気共役点における熱圏風は等しい(赤道横断風モードが卓越する)という仮定のもとで導出される.2 つの手法で観測された夜間の熱圏風を比較するのは本研究が初めてである.2010 年のチェンマイ(タイ)とコトタバン(インドネシア)のイオノゾンデとFPI データを比較した結果,両者はおおむね良い相関を示したが,相関が悪い日もあった.相関が悪い事例は,赤道から収束・発散する成分を無視できず,赤道横断風モードが卓越するという仮定が成立しないと解釈されるものである.また,2 つの手法で求めた熱圏風の相関を季節別に調べると,2-4 月に両者の相関が高い一方,5-7 月に両者の相関が低いことがわかった.

DOI： 10.15094/00009710

CiNii Research

Typhoon-induced concentric airglow structures in the mesopause region Reviewed

S. Suzuki, S. L. Vadas, K. Shiokawa, Y. Otsuka, S. Kawamura, Y. Murayama

GEOPHYSICAL RESEARCH LETTERS Vol. 40 ( 22 ) page： 5983 - 5987 2013.11

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

We present the first reported gravity wave patterns in the mesopause region caused by a typhoon in the troposphere. On 10 December 2002, concentric rings of gravity waves in OH airglow were observed simultaneously by all-sky imagers in the Optical Mesosphere and Thermosphere Imager system in Japan, located at Rikubetsu (43.5 degrees N, 143.8 degrees E), Shigaraki (34.9 degrees N, 136.1 degrees E), and Sata (31.0 degrees N, 130.7 degrees E). The airglow structures, which were well defined and formed a coherent wave pattern expanding concentrically, were identified over 8 h (2135-2947 LT). We estimate the horizontal wavelength, horizontal phase speed, and wave period as 34.5 km, 50.2 m s(-1), and 11.5 min, respectively. Infrared cloud images from the Geostationary Meteorological Satellite show that the center of the rings estimated from the airglow data corresponds to a spiral band of Typhoon Pongsona (T0226). This unique event provides new insight into coupling between the lower and upper atmosphere.

DOI： 10.1002/2013GL058087

Comparison of meridional thermospheric winds observed by ionosondes and Fabry-Perot interferometers Reviewed Open Access

Nishioka M., Maruyama T., Otsuka Y., Tsugawa T., Ishibashi H., Shiokawa K., Ishii M.

Antarctic Record Vol. 57 ( 3 ) page： 357 - 368 2013.11

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

To comprehend ionospheric-thermospheric coupling, one must understand the thermospheric wind system. However, measuring the thermospheric wind using a Fabry-Perot interferometer (FPI) is not an easy task. Because of this difficulty, some researchers have estimated meridional wind velocities using data obtained from a pair of ionosonde stations near the geomagnetic conjugate points, under the assumption that the meridional wind is the same at the two ionosonde stations (transequatorial mode wind). In this paper, we construct the first comparison of the estimated meridional wind velocities with meridional wind observed with FPIs. We analyzed data from the ionosondes and FPIs installed at Chiang Mai, Thailand, and Kototabang, Indonesia, from 2010. We found that the estimated and observed wind velocities were generally in good agreement on most nights, although on some nights, the wind velocities were different. The assumption that the meridional wind is equal anywhere between the two ionosonde stations would not be suitable for the days when the winds were not in good agreement. We also investigated the seasonal dependence of the correlation between the estimated and observed meridional winds. They were in good agreement from February to April and were not in good agreement from May to July. © 2013 National Institute of Polar Research.

DOI： 10.15094/00009710