Faculty Profiles - SHIOKAWA, Kazuo

Geomagnetic conjugate observations of large-scale traveling ionospheric disturbances using GPS networks in Japan and Australia Reviewed Open Access

Takuya Tsugawa, Kazuo Shiokawa, Yuichi Otsuka, Tadahiko Ogawa, Akinori Saito, Michi Nishioka

Journal of Geophysical Research: Space Physics Vol. 111 ( A2 ) 2006.2

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

The geomagnetic conjugacy of large-scale traveling ionospheric disturbances (LSTIDs) was studied using total electron content (TEC) data derived from GPS networks in Japan and Australia. The number of simultaneous occurrences of LSTIDs within ±1 hour in both hemispheres was 5 out of 20 (21) events in Japan (Australia) when Kp ≥ 5- and 0 out of 15 (10) when Kp ≤ 4+. As for the LSTIDs observed simultaneously in both hemispheres, the propagation velocities of equatorward LSTID were comparable between the two hemispheres, with differences of 10-40%. The crossing times at 30° geomagnetic latitude of the simultaneous LSTIDs over Japan and Australia were also different by several tens of minutes for all five events. These observational results indicate that the LSTIDs observed almost simultaneously in both hemispheres are not connected electromagnetically through the geomagnetic field but are generated by atmospheric gravity waves propagating to the equator independently in the two hemispheres. Copyright 2006 by the American Geophysical Union.

DOI： 10.1029/2005JA011300

ERG - A small-satellite mission to investigate the dynamics of the inner magnetosphere Reviewed

Shiokawa K., Seki K., Miyoshi Y., Ieda A., Ono T., Iizima M., Nagatsuma T., Obara T., Takashima T., Asamura K., Kasaba Y., Matsuoka A., Saito Y., Saito H., Hirahara M., Tonegawa Y., Toyama F., Tanaka M., Nose M., Kasahara Y., Yumoto K., Kawano H., Yoshikawa A., Ebihara Y., Yukimatsu A., Sato N., Watanabe S.

MAGNETOSPHERIC DYNAMICS AND THE INTERNATIONAL LIVING WITH A STAR PROGRAM Vol. 38 ( 8 ) page： 1861-1869 2006

Signatures of 3-6 day planetary waves in the equatorial mesosphere and ionosphere Reviewed Open Access

Takahashi H., Wrasse C. M., Pancheva D., Abdu M. A., Batista I. S., Lima L. M., Batista P. P., Clemesha B. R., Shiokawa K.

ANNALES GEOPHYSICAE Vol. 24 ( 12 ) page： 3343 - 3350 2006

GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake Reviewed Open Access

Otsuka Y, Kotake N, Tsugawa T, Shiokawa K, Ogawa T, Effendy, Saito S, Kawamura M, Maruyama T, Hemmakorn N, Komolmis T

EARTH PLANETS AND SPACE Vol. 58 ( 2 ) page： 159 - 165 2006

the Inner Magnetosphere Subgroup in the Society of Geomagnetism and Earth, Planetary and Space Sciences ERG -A small-satellite mission to investigate the dynamics of the inner magnetosphere Reviewed

塩川和夫

Adv. Space Res 38(8) page： 1861 - 1869 2006

Effects of the major geomagnetic storms of October 2003 on the equatorial and low-latitude F region in two longitudinal sectors Reviewed Open Access

Y Sahai, PR Fagundes, F Becker-Guedes, MJA Bolzan, Abalde, JR, VG Pillat, R de Jesus, WLC Lima, G Crowley, K Shiokawa, JW MacDougall, HT Lan, K Igarashi, JA Bittencourt

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A12 ) 2005.12

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

The intense modifications in the ionosphere-thermosphere system in the equatorial and low-latitude regions associated with the dynamic and electrodynamic coupling from high to low latitudes and chemical changes during geomagnetic storms are important space weather issues. In the second half of October 2003, the intense solar activity resulted in one intense and two major geomagnetic storms on 29 and 30 October. In this paper we present and discuss the ionospheric sounding observations carried out from Palmas and Sao Jose dos Campos, Brazil (the Brazilian sector), and Ho Chi Minh City, Vietnam, and Okinawa, Japan (the East Asian sector), during these storms. The two sectors are separated by about 12 hours in local time (so while one sector is in daytime, the other one is in nighttime) and provide valuable information related to the storm-time longitudinal differences. Copious storm-time changes were observed in both sectors. It should be pointed out that the two longitudinal sectors investigated in the present study clearly show the global nature of the storm-time effects. However, the responses to the storm-time effects are also associated with the local time in the two sectors. The present investigations show that there are both similarities and differences in the storm-time response in the two sectors. During the storm main phases, with sharp decreases of the Dst index, both sectors showed (dusk or dawn periods) fast uplifting of the F layer associated with magnetospheric electric field penetration. Although in the East Asian sector, Ho Chi Minh City and Okinawa are located fairly close in longitude, with only 2 hour difference in local lime, on occasions the storm-time responses have been very different. Some differences in the latitudinal response of the F region were also observed in the two sectors. Both positive and negative storm phases have been observed at all the four stations. A comparison of the ionospheric parameters obtained from the TIMEGCM model runs and the observed ionospheric parameters at the four stations shows a reasonable agreement during the quiet periods. During the geomagnetic disturbance period, when there were sharp decreases in Dst, some of the observed rapid uplifts of the F region peak heights are not reproduced by the model results. Also, sometimes the model foF2 results differ considerably from the observed foF2 variations. The period investigated represents an extreme storm situation for validation of the model and points to ways in which the model might be improved in the future.

DOI： 10.1029/2004JA010999

Ground and satellite observations of substorm onset arcs Reviewed Open Access

K Shiokawa, K Yago, K Yumoto, DG Baishev, SI Solovyev, FJ Rich, SB Mende

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A12 ) 2005.12

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

[1] Auroral features and associated particles and fields are investigated for a sequence of substorm onsets observed at similar to 1900 MLT on 24 October 2000. During a 30-min interval at 1020 - 1050 UT, we identified three Pi 2 wave packets with positive H enhancements at midlatitudes and associated auroral brightenings in auroral images obtained by a ground all-sky camera and the IMAGE FUV imager. The DMSP F15 satellite crossed brightening arcs during the third Pi 2 pulsation in the field-of-view of the ground camera at Tixie (66.0 degrees MLAT), Russia. The crossing was 1 - 2 hours duskside of the main onset local time. The brightening arcs were located in the region 1 upward field-aligned current system. The most equatorward arc, which brightened just after the second Pi 2 pulsation, was at the equatorward boundary of the region 1 current and in the sunward convection region. The arcs corresponded to inverted-V accelerated electrons with energies of similar to 10 keV. On the basis of these simultaneous ground-satellite measurements, we discuss substorm onset models of reconnection/ flow braking and near-Earth plasma sheet instabilities.

DOI： 10.1029/2005JA011281

Decrease in B-z prior to the dipolarization in the near-Earth plasma sheet Reviewed Open Access

K Shiokawa, Y Miyashita, Shinohara, I, A Matsuoka

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A9 ) 2005.9

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

[1] We examine in detail the rapid decrease in B-z just before dipolarizations observed by the Geotail satellite in the near-Earth plasma sheet at (X-GSM, Y-GSM) = (-8.3 R-E, - 5.1 R-E). The observations were made using high-time-resolution data from a fluxgate magnetometer (16-Hz sample), a search-coil magnetometer ( 128 Hz), and an electric field antenna ( 64 Hz). Two dipolarizations were observed during a short time interval of 2 min. The magnetic Bz component suddenly decreased 2 - 4 s prior to the dipolarization. Characteristic waves with frequencies of 5 - 20 Hz and amplitudes of 1 - 3 mV m(-1) and 5 - 15 nT s(-1) were observed in the electric and magnetic field data at the time of the sudden decreases in B-z. We discuss two possible causes of the sudden decreases in B-z prior to the dipolarizations: ( 1) passage of a field-aligned line current associated with the substorm current wedge and ( 2) explosive growth phase and subsequent disruption of the tail current caused by the observed characteristic field oscillations.

DOI： 10.1029/2005JA011144

Observations of equatorial plasma bubbles using broadcast VHF radio waves Reviewed Open Access

Nakata, H, Nagashima, I, Sakata, K, Otsuka, Y, Akaike, Y, Takano, T, Shimakura, S, Shiokawa, K, Ogawa, T

GEOPHYSICAL RESEARCH LETTERS Vol. 32 ( 17 ) page： 1 - 4 2005.9

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

The propagation of VHF radio waves affected by field-aligned irregularities within equatorial plasma bubbles is examined. Continuous observation of VHF radio waves at Tateyama, Japan, shows that broadcast radio waves transmitted from Southeast Asia propagate to Japan. Using a ray-tracing calculation combined with a model of scattering by field-aligned irregularities, we determined scatter points suitable for the reception of these radio waves. The results of the calculation show that radio waves transmitted from the Philippines can propagate to Japan owing to field-aligned irregularities within equatorial plasma bubbles located west of Japan. Comparing with all-sky imager data observed at Sata, Japan, we found that the radio waves are received at Tateyama when the plasma bubbles are observed at Sala. The results of this study show that the reception of these radio waves is closely correlated with the equatorial plasma bubbles. Copyright 2005 by the American Geophysical Union.

DOI： 10.1029/2005GL023243