[P-EM15] 太陽地球系結合過程の研究基盤形成

[PEM15-09] Characteristics of CME- and CIR-driven ion upflows in the polar ionosphere

*小川 泰信¹、関 華奈子²、桂華 邦裕²、海老原 祐輔³ (1.国立極地研究所、2.東京大学理学研究科、3.京都大学生存圏研究所)

キーワード：極域電離圏、磁気圏電離圏結合、EISCAT

We investigated how velocity and flux of ionospheric ion upflows vary during magnetic storms driven by corotating interaction regions (CIRs) and coronal mass ejections (CMEs), using data from the European Incoherent Scatter (EISCAT) Tromsø UHF and Svalbard radars between 1996 and 2015. The characteristics of ion upflows were compared with ion and electron temperature variations measured with the EISCAT radars, and also joule heating rate, electric field, and field-aligned current (FAC) distribution derived from the Weimer model. Upward ion velocity increases in the nighttime at Tromsø (66.2 ^o N geomagnetic latitude) just after the CIR- and CME-driven storms, corresponding to electron temperature enhancements due to soft particle precipitation and also ion temperature enhancements in the strong westward electric field region. The CME-driven storms have larger upward ion flux (~1.7×10¹³ m^-2s^-1) than those under the CIR-driven storms (~0.3×10¹³ m^-2s^-1). In the daytime, ion upflows are seen at Longyearbyen, Svalbard (75.2 ^o N geomagnetic latitude), with an upward flux of typically 10¹³ m^-2s^-1 for small CIR and CME storm cases. Substantial ion upflows last for a few days after the storm onsets under small CIR storms, whereas they last for only a day under small CME storms. Under both the cases, the substantial ion upflows are associated with an enhancement of the Region 1 FAC, eastward electric field and Joule heating rate. For large CME storms, substantial ion upflows are absent in the daytime probably due to equatorward expansion of the auroral oval.