R006-11
Zoom meeting B ：11/1 PM1 (13:45-15:30)
14:00〜14:15

Contribution of magnetospheric pressure inhomogeneities to SAPS Wave Structures: Arase and SuperDARN conjugated observations#Takehiro Fukami1) ,Atsushi Kumamoto2) ,Yuto Katoh1) ,Nozomu Nishitani3) ,Tomoaki Hori3) ,Yasumasa Kasaba4) ,Fuminori
Tsuchiya2) ,Mariko Teramoto5) ,Tomoki Kimura6) ,Yoshiya Kasahara7) ,Masafumi Shoji3) ,Satoko Nakamura8) ,Masahiro Kitahara3) ,Ayako Matsuoka9) ,Shun Imajo10) ,Satoshi Kasahara11) ,Shoichiro Yokota12) ,Kunihiro Keika13) ,Yoichi Kazama14) ,Shiang-Yu
Wang15) ,ChaeWoo Jun16) ,Kazushi Asamura17) ,Yoshizumi Miyoshi3) ,Iku Shinohara18) ,Simon G. Shepherd19)(1Dept. Geophys., Grad. Sch. Sci., Tohoku Univ.,(2 Planet. Plasma Atmos. Res. Cent., Tohoku Univ.,(3 ISEE, Nagoya
Univ.,(4 Tohoku Univ.,(5 Kyutech,(6 Tokyo University of Science,(7 Kanazawa Univ.,(8 ISEE,(9 Kyoto University,(10 ISEE, Nagoya
Univ.,(11 The University of Tokyo,(12 Osaka Univ.,(13 University of Tokyo,(14 ASIAA,(15 Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan,(16 ISEE, Nagoya Univ.,(17 ISAS/JAXA,(18 ISAS/JAXA,(19 Dartmouth College
Contribution of magnetospheric pressure inhomogeneities to SAPS Wave Structures (SAPSWS) is investigated on the basisof the case analyses of conjugated Arase satellite and SuperDARN observations.
Erickson et al. (2002) reported substructures with a scale size of tens of km within SAPS. Mishin and Burke (2005) called
them ”SAPSWS”, and reported that high-temperature ions were transported into the inner magnetosphere and showed energy
dispersion (ion nose structure) when the electromagnetic field fluctuations of SAPSWS were observed. Using the numericalsimulation of hot plasma dynamics in the inner magnetosphere coupled with the ionosphere, Ebihara et al. (2009) showedthat hot plasma with a complex pressure distribution could contribute to variations of SAPS.
Further detailed comparisons among electromagnetic field and hot ions in the magnetosphere and flow in the ionosphere
are important for understanding the mechanism of SAPSWS. So, We analyzed data from conjugate Arase and SuperDARN
Christmas Valley East (CVE) radar observations during 2:30 to 3:00 UT on 9 July 2017.
From the CVE radar observation, we obtained 2-dimensional flow distributions of SAPSWS with velocity fluctuations of200 m/s near the ionospheric footprint of Arase, assuming that the flows are zonally-directed. These structures extended overat least 0.5 h MLT azimuthally, separated latitudinally at intervals of ˜230 km, and moved equatorward. Near the magneticequator, Arase encountered electric field variations with an amplitude of 2.5 mV/m and a period of 5-6 minutes in the ion
nose structure, during an outbound pass from L = 3.2 to 5.4 around 20 h MLT. The isotropic pressure of hot ions was derived from ion flux in an energy range of 10-180 keV. Variations of the eastward magnetic field and the ion pressure wereroughly in phase and had a close period to that of the electric field variations. The phase relation and flow distribution in theionosphere suggested that earthward hot ions with fine pressure inhomogeneities generate field-aligned currents in the innermagnetosphere and thereby cause SAPSWS.
We consider substorm-related plasma sheet flow channels [e.g. Lyons et al. (2012)] and interchange instability in the innermagnetosphere [Sazykin et al. (2002)] could generate such pressure inhomogeneities in the magnetosphere. In conjugate
Arase and SuperDARN observation event, GOES-13 observed dipolarization and an increase of proton flux around 21 h MLT
at 2:19 UT. Equatorial projection of ionospheric flow structures along the magnetic field given by the Tsyganenko 04s model(T04s model; Tsyganenko & Sitnov, 2005) moved earthward from L˜6 to ˜4 during 2:30 to 3:00 UT. The movement may
reflect earthward transportation of hot plasma driving fine-scale ionospheric flow. These results imply that substorm injectionpossibly contributes to the formation of pressure inhomogeneities in the inner magnetosphere and SAPSWS.