Faculty Profiles - SHIOKAWA, Kazuo

プラズマバブル発生に伴う全電子数変化率の緯度依存性

Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs Reviewed

Nishimura Y., Lyons L. R., Shiokawa K., Angelopoulos V., Donovan E. F., Mende S. B.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 118 ( 5 ) page： 2034 - 2042 2013.5

鈴木順也, 中田裕之, 鷹野敏明, 津川卓也, 斉藤昭則, 大塚雄一, 塩川和夫

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 7 ( 1 ) page： 60 - 61 2013.4

Evidence of gravity wave ducting in the mesopause region from airglow network observations Reviewed Open Access

Suzuki, S, Shiokawa, K, Otsuka, Y, Kawamura, S, Murayama, Y

GEOPHYSICAL RESEARCH LETTERS Vol. 40 ( 3 ) page： 601 - 605 2013.2

Ground and satellite observations of low-latitude red auroras at the initial phase of magnetic storms Reviewed Open Access

K. Shiokawa, Y. Miyoshi, P. C. Brandt, D. S. Evans, H. U. Frey, J. Goldstein, K. Yumoto

Journal of Geophysical Research: Space Physics Vol. 118 ( 1 ) page： 256 - 270 2013.1

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

We report ground and satellite observations of unique low-latitude red auroras that appear at the initial phase of geomagnetic storms. For two events on 21 October 2001, and 6 April 2000, the low-latitude red auroras appeared at ∼45° MLAT (L ∼ 2) ∼ 1.5 h after the storm sudden commencement in the postmidnight sector in Japan. Comprehensive satellite data were available for the former event. The energetic neutral atom images obtained by the Imager for Magnetopause-to-Aurora Global Exploration satellite show rapid enhancement of ring current hydrogen and oxygen fluxes at radial distances of ∼ 2-8 RE after the storm sudden commencement and associated with several storm-time substorms. The hydrogen ring-current enhancement occurred particularly in the postmidnight sector where the red aurora was observed. The timing of oxygen flux enhancement associated with a storm-time substorm coincided with the red aurora appearance. This rapid and significant enhancement of energetic neutral atom flux was also confirmed by energetic ion data obtained by the NOAA/POES-16 satellite. Extreme ultraviolet plasmaspheric images obtained by Magnetopause-to-Aurora Global Exploration indicate that the plasmapause was located at L = 2.3-2.5 in the postmidnight sector during the event, indicating that a spatial overlap occurs between the plasmasphere and the enhanced ring current ions at L ∼ 2. Based on these observations, we suggest that large energization of high-energy ring-current ions in the postmidnight inner magnetosphere caused the spatial overlap of these ring-current ions with the low-energy plasmaspheric plasmas at L ∼ 2, producing the low-latitude red auroras at the very beginning of the storms. ©2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA018001

Geomagnetic conjugate observations of plasma-sheet electrons by the FAST and THEMIS satellites Reviewed Open Access

S. Lee, K. Shiokawa, J. P. McFadden, K. Seki

Journal of Geophysical Research: Space Physics Vol. 118 ( 1 ) page： 132 - 145 2013.1

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

We investigate pitch-angle distributions and spectral shapes of auroral electrons simultaneously observed during three conjunction events by the FAST satellite at altitudes of 2500-3500 km and by the THEMIS satellite in the plasma sheet at 7-13 RE. All three events were on the lower latitude of the auroral oval. Conjunction event 1 occurred at ~1914:45 UT on 10 April 2008. Electron spectra at energies of 0.1-3 keV are correlated well between the two satellites, while the precipitating electrons above 3 keV are missing at FAST. Event 2 occurred at 1255:26 UT on 26 April 2008. Electron spectra above 3 keV are correlated well between the two satellites. An additional broad spectral peak at energies of 0.1-0.5 keV was observed by FAST. Event 3 occurred at 0058:04 UT on 25 December 2008. Precipitating electrons of 0.5-5 keV obtained by FAST are correlated well with those of THEMIS-C, while a monoenergetic peak at 0.1-0.2 keV was observed only by FAST. For the three conjunction events, we conclude that high-energy precipitating auroral electrons observed by FAST directly come from the equatorial plasma sheet, while low-energy precipitating electrons may come from middle altitudes as a result of acceleration by static potential differences. For missing high-energy (&gt
3 keV) electrons of event 1, we speculate that the pitch-angle scattering by waves occurs only at a limited energy range. ©2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017805

GPS observations of medium-scale traveling ionospheric disturbances over Europe Reviewed Open Access

Otsuka, Y, Suzuki, K, Nakagawa, S, Nishioka, M, Shiokawa, K, Tsugawa, T

ANNALES GEOPHYSICAE Vol. 31 ( 2 ) page： 163 - 172 2013

Stereoscopic determination of all-sky altitude map of aurora using two ground-based Nikon DSLR cameras Reviewed Open Access

R. Kataoka, Y. Miyoshi, K. Shigematsu, D. Hampton, Y. Mori, T. Kubo, A. Yamashita, M. Tanaka, T. Takahei, T. Nakai, H. Miyahara, K. Shiokawa

ANNALES GEOPHYSICAE Vol. 31 ( 9 ) page： 1543 - 1548 2013

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

A new stereoscopic measurement technique is developed to obtain an all-sky altitude map of aurora using two ground-based digital single-lens reflex (DSLR) cameras. Two identical full-color all-sky cameras were set with an 8 km separation across the Chatanika area in Alaska (Poker Flat Research Range and Aurora Borealis Lodge) to find localized emission height with the maximum correlation of the apparent patterns in the localized pixels applying a method of the geographical coordinate transform. It is found that a typical ray structure of discrete aurora shows the broad altitude distribution above 100 km, while a typical patchy structure of pulsating aurora shows the narrow altitude distribution of less than 100 km. Because of its portability and low cost of the DSLR camera systems, the new technique may open a unique opportunity not only for scientists but also for night-sky photographers to complementarily attend the aurora science to potentially form a dense observation network.

DOI： 10.5194/angeo-31-1543-2013

Special Issue: Recent Progress in the Vertical Coupling in the Atmosphere-Ionosphere System Preface Reviewed

Drift velocities of 150-km field-aligned irregularities observed by the equatorial atmosphere radar Reviewed Open Access

Otsuka Y, Mizutani N, Shiokawa K, Patra A, Yokoyama T, Yamamoto M

Antarctic Record Vol. 57 ( 3 ) page： 369 - 378 2013

Giant ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GPS network after the 2011 Tohoku earthquake Reviewed Open Access

Ogawa Tadahiko, Nishitani Nozomu, Tsugawa Takuya, Shiokawa Kazuo

EARTH PLANETS AND SPACE Vol. 64 ( 12 ) page： 1295-1307 2012.12

Dora Pancheva, Kazuo Shiokawa, Petra Knizova, Weixing Wan

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 90-91 ( 1 ) page： V - VI 2012.12

Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies Reviewed Open Access

K. Shiokawa, Y. Otsuka, S. Oyama, S. Nozawa, M. Satoh, Y. Katoh, Y. Hamaguchi, Y. Yamamoto, J. Meriwether

EARTH PLANETS AND SPACE Vol. 64 ( 11 ) page： 1033 - 1046 2012.11

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

We have developed new Fabry-Perot interferometers (FPIs) that are designed to measure thermospheric winds and temperatures as well as mesospheric winds through the airglow/aurora emissions at wavelengths of 630.0 nm and 557.7 nm, respectively. One FPI (FP01), possessing a large aperture etalon (diameter: 116 mm), was installed at the EISCAT Tromso site in 2009. The other FPIs, using 70-mm diameter etalons, were installed in Thailand, Indonesia, and Australia in 2010-2011 (FP02-FP04) by the Solar-Terrestrial Environment Laboratory, and in Peru (Nazca and Jicamarca) and Alaska (Poker Flat) by Clemson University. The FPIs with 70-mm etalons are low-cost compact instruments, suitable for multipoint network observations. All of these FPIs use low-noise cooled-CCD detectors with 1024 x 1024 pixels combined with a 4-stage thermoelectric cooling system that can cool the CCD temperature down to -80 degrees C. The large incident angle (maximum: 1.3 degrees-1.4 degrees) to the etalon achieved by the use of multiple orders increases the throughput of the FPIs. The airglow and aurora observations at Tromso by FP01 show wind velocities with typical random errors ranging from 2 to 13 m s(-1) and from 4 to 27 m s(-1) for mesosphere (557.7 nm) and thermosphere (630.0 nm) measurements, respectively. The 630.0-nm airglow observations at Shigaraki, Japan, by FP02-FP04 and by the American FPI instruments give thermospheric wind velocities with typical random errors that vary from 2 m s(-1) to more than 50 m s(-1) depending on airglow intensity.

DOI： 10.5047/eps.2012.05.004

Reflection height of daytime tweek atmospherics during the solar eclipse of 22 July 2009 Reviewed Open Access

Hiroyo Ohya, Fuminori Tsuchiya, Hiroyuki Nakata, Kazuo Shiokawa, Yoshizumi Miyoshi, Kozo Yamashita, Yukihiro Takahashi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 11 ) 2012.11

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

We report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 July 2009. Sixteen and sixty-three tweek atmospherics were observed at Moshiri and Kagoshima, Japan, where the magnitudes of the solar eclipse were 0.458 and 0.966, respectively. This was the first observation of tweek atmospherics during a low-magnitude eclipse (0.458). The average and standard deviation of the reflection height were 94.9 +/- 13.7 km at Moshiri and 87.2 +/- 12.9 km at Kagoshima. The reflection height at Moshiri was almost the same as that for normal nighttime conditions in July (96.7 +/- 12.6 km) in spite of the low magnitude of the eclipse. The reflection height at Kagoshima seems be divided into two parts: propagation across the total solar eclipse path and propagation in the partial solar eclipse path. During the eclipse, we also observed the phase variation in the LF transmitter signals. The average change in the phase delay of the LF signals was 109 degrees for the paths that crossed the eclipse path and 27 degrees for the paths that did not cross the eclipse path. Assuming a normal daytime height for LF waves of 65 km, a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5-6 km for the paths across the eclipse and 1-2 km for partial eclipse paths. The wide range of estimated tweek reflection heights at Kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses.

DOI： 10.1029/2012JA018151

Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years Reviewed Open Access

D. Fukushima, K. Shiokawa, Y. Otsuka, T. Ogawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

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

We report on nighttime medium- scale traveling ionospheric disturbances (MSTIDs) observed at Kototabang, Indonesia (geographic longitude: 100.3 degrees E; geographic latitude: 0.2 degrees S; and geomagnetic latitude: 10.6 degrees S) during a 7-year period from October 2002 to October 2009. MSTIDs were observed in 630-nm nighttime airglow images by using a highly sensitive all-sky airglow imager at Kototabang. The averages and standard deviations of horizontal phase velocity, period, and horizontal wavelength of MSTIDs observed during the 7 years were 320 +/- 170 m/s, 42 +/- 11 min, and 790 +/- 440 km, respectively. The occurrence rate of the observed MSTIDs decreased with decreasing solar activity. The average horizontal wavelength of MSTIDs increased with decreasing solar activity. Southward MSTIDs were dominant throughout the 7 years of observations. These facts are consistent with the hypothesis that the observed MSTIDs are caused by gravity waves in the thermosphere. Moreover, we compared the propagation directions of the observed MSTIDs with the locations of tropospheric convection activity for the events where gravity waves producing the observed MSTIDs could have existed in the lower atmosphere. Strong tropospheric convection was found within +/- 30 degrees from the source directions of MSTIDs in 81% of the MSTID events. In such events, gravity waves were possibly generated from deep convection in the troposphere and directly propagated into the thermosphere.

DOI： 10.1029/2012JA017758

Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening Reviewed Open Access

Shiokawa, K, Mori, M, Otsuka, Y, Oyama, S, Nozawa, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

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

We report for the first time the rapid oscillating motion of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) based on airglow imaging observations at Tromso (magnetic latitude: 67.1 degrees N), Norway on 8 December, 2009. The MSTIDs appeared in 630-nm airglow images at 1530 UT as wave-like structures south of Tromso with a horizontal wavelength of similar to 200 km and a phase surface of north to south. They moved eastward with velocities of 30-60 m/s. The velocity was faster in the poleward-side of the MSTIDs, forming a northeast-southwest phase surface at later times. This phase surface direction is opposite to that of midlatitude MSTIDs. The MSTIDs show sudden oscillations and phase jump in the east-west direction with a timescale of similar to 10 min at 1730 UT. The oscillations were associated with an auroral brightening observed at the poleward edge of the images and small magnetic field perturbations observed by ground magnetometers. The Doppler measurement of the 630-nm airglow by a Fabry-Perot interferometer at Tromso showed a stable southeastward thermospheric wind with a velocity of similar to 150 m/s. These observations indicate that the MSTID oscillations were linked to auroral electric field in the ionosphere, implying that the observed MSTIDs are ionospheric plasma structures. We suggest that the observed MSTIDs were created by atmospheric gravity waves at the beginning, left as fossil plasma structures even after the gravity wave packet dissipated in the thermosphere, moved eastward according to the background electric field driven by the F-region dynamo, and oscillated associated with the auroral electric field.

DOI： 10.1029/2012JA017928

Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008 Reviewed

K-H Kim, D-H Lee, K. Shiokawa, E. Lee, J-S Park, H-J Kwon, V. Angelopoulos, Y-D. Park, J. Hwang, N. Nishitani, T. Hori, K. Koga, T. Obara, K. Yumoto, D. G. Baishev

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

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

The passage of an interplanetary (IP) shock was detected by Wind, ACE, Geotail, and THEMIS-B in the solar wind on 24 November 2008. From the propagation time of the IP shock at the spacecraft, it is expected that the IP shock front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using multipoint observations of the sudden commencement (SC) at THEMIS probes, GOES 11, and ETS in the dayside magnetosphere, we confirmed that the magnetospheric response to the IP shock starts earlier in the postnoon sector than in the prenoon sector. We found that the estimated normal direction of the SC front is nearly aligned with the estimated IP shock normal. We also found that the SC front normal speed is much slower than the fast mode speed and is about 22-56% of the IP shock speed traveling in the solar wind. Thus, we suggest that the major field changes of the SC in the dayside magnetosphere are not due to the magnetic flux carried by hydromagnetic waves but to the increased solar wind dynamic pressure behind the shock front sweeping the magnetopause. The SC event appears as a step-like increase in the H component at the low-latitude Bohyun station and a negative-then-positive variation in the H component at the high-latitude Chokurdakh (CHD) station in the morning sector. During the negative perturbation at CHD, the SuperDARN Hokkaido radar detected a downward motion in the ionosphere, implying westward electric field enhancement. Using the THEMIS electric field data, it is confirmed that the westward electric field corresponds to the inward plasma motion in the dayside magnetosphere due to the magnetospheric compression.

DOI： 10.1029/2012JA017871

Visualization of ion cyclotron wave and particle interactions in the inner magnetosphere via THEMIS-ASI observations Reviewed Open Access

K. Sakaguchi, Y. Miyoshi, E. Spanswick, E. Donovan, I. R. Mann, V. Jordanova, K. Shiokawa, M. Connors, J. C. Green

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

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

Interaction with EMIC (electromagnetic ion cyclotron) waves is thought to be a key component contributing to the very rapid loss of both ring current and radiation belt particles into the atmosphere. Estimated loss rates are heavily dependent on the assumed spatial distribution of the EMIC wave. Statistical maps of the spatial distribution have been produced using in-situ satellite data. However, with limited satellite data it is impossible to deduce the true spatial distribution. In this study, we present ground-based observations using all-sky imager and search coil magnetometer networks, which provide the large-scale distribution and motion of the EMIC wave-particle interaction regions. We observed several spots of isolated proton auroras simultaneously with Pc1/EMIC waves at subauroral latitudes during the expansion phase of a storm-time substorm on 9 March 2008. The isolated auroras were distributed over similar to 4-hours MLT preceding midnight. The POES-17 satellite confirmed enhancements of 30-keV proton precipitations over the isolated auroras. The equatorward motion of the auroras and frequency drift of the wave were consistent with the plasmasphere eroding due to a polar cap potential enhancement modeled by a numerical simulation. We also found that relativistic electron precipitation was not always associated with the isolated aurora, depending strongly on the plasma density profile near the plasmapause. This study shows that the specific distribution of ring current proton precipitation can be visualized through the ground network observations. By combining with upcoming inner-magnetosphere satellite missions, these remote-sensing observations are very important for quantitative understanding of the particle loss in the inner magnetosphere.

DOI： 10.1029/2012JA018180