Faculty Profiles - SHIOKAWA, Kazuo

Simultaneous THEMIS in situ and auroral observations of a small substorm Reviewed

E. Donovan, W. Liu, J. Liang, E. Spanswick, I. Voronkov, M. Connors, M. Syrjasuo, G. Baker, B. Jackel, T. Trondsen, M. Greffen, V. Angelopoulos, C. T. Russell, S. B. Mende, H. U. Frey, A. Keiling, C. W. Carlson, J. P. McFadden, K. -H. Glassmeier, U. Auster, K. Hayashi, K. Sakaguchi, K. Shiokawa, J. A. Wild, I. J. Rae

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 17 ) 2008.8

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

We present ground-based and in situ observations from March 13, 2007. The THEMIS satellites were in the evening sector conjugate to THEMIS ground-based imagers. At similar to 0507 UT there was an optical onset on inner CPS field lines. This involved near-simultaneous brightening of 1 MLT hour longitudinal segment of the onset arc. The part of the arc that brightened was that closest to the equatorward boundary of the diffuse ( proton) aurora. Within one minute, a dipolarization front moved across four THEMIS satellites. Based on their locations, the order in which they detected the dipolarization front, and the auroral evolution, we assert that the expansion phase began earthward of the four satellites and evolved radially outwards. We conclude that this onset occurred in an azimuthally localized region of highly stretched field lines.

DOI： 10.1029/2008GL033794

Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms: A multievent study Reviewed Open Access

A. Nakajima, K. Shiokawa, K. Seki, J. P. McFadden, C. W. Carlson, R. J. Strangeway, K. Yumoto

Journal of Geophysical Research: Space Physics Vol. 113 ( A6 ) 2008.6

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

During geomagnetic storms, remarkable electron-flux enhancements (&gt
1012 eV cm-2 s-1) over a broadband energy range (∼0.05-10 keV) are sometimes observed near the equatorward edge of the auroral oval. We call such electron flux enhancements broadband electrons (BBEs). In this paper, we identified 12 BBE events from the electron-energy spectra obtained by the Fast Auroral Snapshot (FAST) satellite during 81 large geomagnetic storms (minimum Dst index &lt
-90 nT) between September 1996 and March 2004. Ground-based magnetic field data show that the BBEs are observed ∼6-28 min after the onset of substorms during the main phase of large storms. During these events, the pitch angle distributions of electrons show isotropic features at a higher energy range above ∼1 keV, except for an upward loss cone. At a lower energy range below ∼1 keV, field-aligned downward electron fluxes are most intense, and perpendicular fluxes are weakest. These results imply that a higher-energy part of BBEs originates from higher altitudes in the inner magnetosphere and that a lower-energy part is accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields and enhanced lower-frequency (0.1 Hz to 16 kHz) waves are observed during the BBEs. These characteristics are common for all BBE events. We compared lower-energy (&lt
1 keV) electron fluxes with field-aligned Poynting fluxes of the waves at 0.06-4 Hz during the BBEs. The Poynting fluxes are systematically downward with intensity comparable to that of the lower-energy electron fluxes, suggesting downward acceleration of lower-energy electrons by the observed low-frequency waves. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA013001

Correlation of substorm injections, auroral modulations, and ground Pi2 Reviewed Open Access

A. Keiling, V. Angelopoulos, D. Larson, R. Lin, J. McFadden, C. Carlson, J. W. Bonnell, F. S. Mozer, K. -H. Glassmeier, H. U. Auster, W. Magnes, S. Mende, H. Frey, A. Roux, O. LeContel, S. Frey, T. Phan, E. Donovan, C. T. Russell, I. Mann, W. Liu, X. Li, M. Fillingim, G. Parks, K. Shiokawa, J. Raeder

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 17 ) 2008.6

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

In this case study we report a substorm, 23 March 2007, which exhibited oscillations with a period of similar to 135 s in three substorm phenomena all of which were one-to-one correlated. The in-situ observations are from one THEMIS spacecraft (8.3 R(E) geocentric distance) and the geosynchronous LANL-97A spacecraft. The focus here is on the intensification phase during which THEMIS was conjugate to the region of auroral brightening and its foot point was near the high-latitude ground station Kiana. The following results will be demonstrated: (1) THEMIS and LANL-97A (time-delayed) recorded periodic ion injections (> 100 keV). (2) Near-conjugate high-latitude ground magnetometer data show very large Pi2 (delta H similar to 150\ nT) with a 6-s time delay compared to the THEMIS ion injections. (3) Low-latitude ground magnetometer data also show Pi2 with the same waveform as the high-latitude Pi2 but with longer time delays (20-31 s). (4) Auroral luminosity was periodically modulated during the intensification phase. (5) All three signatures (ion injections, ground Pi2, optical modulation) had the same periodicity of similar to 135 s but with various time delays with respect to the THEMIS ion injections. These observations demonstrate that the three substorm phenomena had a common source which controlled the periodicity.

DOI： 10.1029/2008GL033969

プラズマバブルの発生位置の同定 Reviewed

木下佳紀, 中田裕之, 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 Vol. 2 ( 1 ) page： 147 - 148 2008.5

Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes Reviewed Open Access

K. Sakaguchi, K. Shiokawa, Y. Miyoshi, Y. Otsuka, T. Ogawa, K. Asamura, M. Connors

Journal of Geophysical Research: Space Physics Vol. 113 ( A5 ) 2008.5

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

We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude (magnetic latitude: 62°, L ∼ 4.6), using an all-sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (H β) were often observed at latitudes separated equatorward from the main auroral oval. From a 1-year observation (4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre- and post-midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250-800 km, respectively. We found that as isolated arcs moved equatorward (poleward), the frequencies of the simultaneous Pc 1 pulsations increased (decreased). Using the Tsyganenko-02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron (EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high-energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low-latitude auroral emissions away from the ordinary auroral oval. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA012888

Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow Reviewed

Suzuki H., Shiokawa K., Tsutsumi M., Nakamura T., Taguchi M.

Polar Science Vol. 2 ( 1 ) page： 1 - 8 2008.3

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

Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2-6% in intensity and 0.5-2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O2 and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474]. © 2008 Elsevier B.V. and NIPR.

DOI： 10.1016/j.polar.2007.12.002

Optical and radio observations and AMIE/TIEGCM modeling of nighttime traveling ionospheric disturbances at midlatitudes during geomagnetic storms

Fluctuation of intensity and rotational temperature of OH airglow caused by acoustic gravity waves Reviewed

Suzuki, H, K. Shiokawa, M. Tsutsumi, T. Nakamura, M. Taguchi

Polar Sci. Vol. 2 page： 1 - 8 2008.1

Development of an automatic procedure to estimate the reflection height of tweek atmospherics Reviewed Open Access

Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

EARTH PLANETS AND SPACE Vol. 60 ( 8 ) page： 837 - 843 2008

Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms Reviewed Open Access

Koustov A., Hosokawa K., Nishitani N., Ogawa T., Shiokawa K.

ANNALES GEOPHYSICAE Vol. 26 ( 9 ) page： 2711-2723 2008

K. Shiokawa, T. Tsugawa, T. Tsugawa, Y. Otsuka, T. Ogawa, G. Lu, A. Saito, M. Yamamoto

Geophysical Monograph Series Vol. 181 page： 271 - 281 2008

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

© 2008 by the American Geophysical Union. This paper summarizes our recent observations of storm-time traveling ionospheric disturbances (TIDs) over Japan. The storm-time TIDs, which are often referred as large-scale TIDs or traveling atmospheric disturbances, are generated at high-latitude auroral zone and propagate predominantly equatorward at midlatitudes as atmospheric waves in the thermosphere. The imaging measurements by airglow imagers and GPS networks give reliable wave parameters (wavelength, phase velocity, and amplitude) of TIDs. Comparison of imaging observations of TIDs between the northern and southern hemispheres revealed their nonconjugacy. Combinations of these imaging observations with vertical sounding measurements by ionosondes and radars provide a comprehensive description of TID structures at midlatitudes. Comparison between these observations and the assimilative mapping of the ionospheric electrodynamics technique with the thermosphere-ionosphere electrodynamics general circulation model results in several insights into the generation and propagation of TIDs at the high-latitude source region as well as limitations of the current global model.

DOI： 10.1029/181GM24

Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E region field-aligned irregularities at midlatitude Reviewed Open Access

Otsuka, Y, Onoma, F, Shiokawa, K, Ogawa, T, Yamamoto, M, Fukao, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 112 ( A6 ) 2007.6

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

We report on simultaneous observations of very high frequency (VHF) radar backscatter from field-aligned irregularities (FAI) in the E region and medium-scale traveling ionospheric disturbances (MSTID) in 630-nm airglow images. On the night of 6 August 2002, the powerful 46.5-MHz middle and upper atmosphere (MU) radar with five beam directions at Shigaraki, Japan, observed typical quasiperiodic (QP) echoes from FAI in the E region. During this QP echo event, an all-sky charge-coupled device imager at the MU radar site detected MSTID in 630-nm airglow images. The MSTID also propagated southwestward at 80 m/s with fluctuation amplitudes of 50% from the background intensity and a wavelength of 380 km. Period of the MSTID was almost same as that of the Doppler velocity in the QP echoes. The airglow enhancement (depletion) caused by the MSTID coincided with southeastward (northwestward) velocity in the QP echo. These results indicate that the electric fields associated with the F region MSTID could be closely coupled to those associated with QP echoes in the E region. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2005JA011548

Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm Reviewed Open Access

A. Nakajima, K. Shiokawa, K. Seki, R. J. Strangeway, J. P. McFadden, C. W. Carlson

Journal of Geophysical Research: Space Physics Vol. 112 ( A6 ) 2007.6

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

Broadband electrons (BBEs) are remarkable flux enhancements (&gt
10 13 eV cm-2 s-1) of precipitating electrons over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. We show characteristics of particles (energy spectra and pitch angle distribution) and fields (electric field, magnetic field, and wave spectra) during a BBE event observed by the Fast Auroral SnapshoT (FAST) satellite. The BBEs were observed at an altitude of ∼2000 km at 59°-61° invariant latitudes (ILATs) and 21 h magnetic local time (MLT). The event was observed at ∼7 min after the onset of a substorm during the main phase of the Bastille Day geomagnetic storm (minimum Dst = -301 nT) on 15 July 2000. The precipitation region of the BBEs corresponded to a localized intensification of auroral emission, lasting ∼14 min, observed by the Polar UVI images at 50°-60° geomagnetic latitudes (MLATs) and 20-21 MLTs. These results suggest that rapid particle acceleration was occurring in the inner magnetosphere associated with a storm-time substorm. The pitch angle distribution of BBEs was isotropic except for a loss cone feature around the field-aligned upward direction at a higher energy range above ∼1 keV, while field-aligned electron fluxes were larger than the perpendicular fluxes below ∼1 keV. These results imply that a higher energy part of the BBEs originated from higher altitudes in the inner magnetosphere and that a lower energy part was accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields were observed during this BBE event. From these results, we discuss possible acceleration of the lower energy part of BBEs through wave-particle interaction. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012184

Signatures of ultra fast Kelvin waves in the equatorial middle atmosphere and ionosphere Reviewed Open Access

H. Takahashi, C. M. Wrasse, J. Fechine, D. Pancheva, M. A. Abdu, I. S. Batista, L. M. Lima, P. P. Batista, B. R. Clemesha, N. J. Schuch, K. Shiokawa, D. Gobbi, M. G. Mlynczak, J. M. Russell

GEOPHYSICAL RESEARCH LETTERS Vol. 34 ( 11 ) 2007.6

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

In the equatorial atmosphere, oscillations with periods of 3 to 4 days have been observed in the meteor radar zonal wind at Cariri ( 7.4 degrees S, 36.5 degrees W), in the ionospheric minimum virtual height h'F and the maximum critical frequency foF2 at Fortaleza (3.9 degrees S, 38.4 degrees W), and in the TIMED/SABER satellite temperature data in the stratosphere-mesosphere. Wavelet analyses of these time series reveal that the 3-4-day oscillation was observed for all of these data during the period from March 1 to 11, 2005. From the characteristics of the downward phase propagation ( wavelength of similar to 40 km), longitudinal and latitudinal extension, we conclude that this oscillation must be a 3.5-day Ultra Fast Kelvin (UFK) wave. This is the first report of clear evidence of propagation of a UFK wave from the stratosphere to the ionosphere. The UFK wave could have an important role in the day-to-day variability of the equatorial ionosphere evening uplift.

DOI： 10.1029/2007GL029612

Ground observation and AMIE-TIEGCM modeling of a storm-time traveling ionospheric disturbance Reviewed Open Access

Shiokawa, K, Lu, G, Otsuka, Y, Ogawa, T, Yamamoto, M, Nishitani, N, Sato, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 112 ( A5 ) 2007.5

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

This paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high-latitude energy input based on data assimilation. A prominent traveling ionospheric disturbance (TID) was observed during the major magnetic storm of 31 March 2001. The TID propagated from north to south over Japan with phase speeds of 370-640 m/s. The assimilative mapping of ionospheric electrodynamics (AMIE) technique was used as input to the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) to investigate generation and propagation of the observed TID. In the model, two Joule heating enhancements in the high-latitude dayside sector produced two distinct traveling atmospheric waves (TADs), which propagated to Japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed. The phase speed of the TADs was much faster (∼1100 m/s) in the model, probably due to the overestimation of Joule heating in the model. The second TAD corresponds to the observed prominent TID, while signatures of the first TAD were also seen in the observed ionosonde data. The observed TID was characterized by a decrease in southward wind speed, causing a significant F-layer height decrease and a temporal enhancement of F-layer peak density. These characteristics were reproduced by the model as a rarefaction of the second TAD. The temporal enhancement of F-layer peak density was because of the vertical shear of meridional wind. The absolute value of F-layer electron density in the model was several factors smaller than that observed, probably because of the underestimation of the supply of O+ ions from the plasmasphere. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA011772

An intense gravity wave near the mesopause region observed by a Fabry-Perot interferometer and an airglow imager Reviewed Open Access

Shiokawa, K, Suzuki, S, Otsuka, Y, Ogawa, T, Nakamura, T, Horinouchi, T

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 112 ( D7 ) 2007.4

Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes Reviewed Open Access

K. Sakaguchi, K. Shiokawa, A. Leda, Y. Miyoshi, Y. Otsuka, T. Ogawa, M. Connors, E. F. Donovan, F. J. Rich

Journal of Geophysical Research: Space Physics Vol. 112 ( A4 ) 2007.4

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

We observed an isolated proton arc at the Athabasca station (MLAT: 62°N) in Canada on 5 September 2005, using a ground-based all-sky imager at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (Hβ). This arc is similar to the detached proton arc recently observed by the IMAGE satellite [Immel et al., 2002]. The arc appeared at 0500-0640 UT (2100-2240 MLT), coincident with strong Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. The isolated arc did not change its structure and intensity during the late growth and expansive phases of a small substorm that occurred at 0550 UT. From particle data obtained by the NOAA 17 satellite, we found that the isolated arc was associated with the localized enhancement of ion precipitation fluxes at an energy range of 30-80 keV at L ~ 4. Trapped ion flux enhancements (ring current ions) were also observed at two latitudinally separated regions. The localized ion precipitation was located at the outer boundary of the inner ring current ions. The DMSP F13 satellite observed signatures of an ionospheric plasma trough near the conjugate point of the arc in the Southern Hemisphere. The trough is considered to be connected to the plasmapause. These results indicate that the source region of the isolated arc was located near the plasmapause and in the ring current. We conclude that the observed isolated proton arc at subauroral latitudes was caused by the EMIC waves, which were generated near the plasmapause and resonantly scattered the ring current protons into the loss cone. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012135