[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-14] Geomagnetic Activity Dependence of High-Altitude Upflowing Ion Beam Observed by the Arase Satellite

*今城 峻¹、三好 由純²、浅村 和史³、篠原 育³、能勢 正仁²、塩川 和夫²、松岡 彩子¹、堀 智昭²、寺本 万里子⁴ (1.京都大学、2.名古屋大学、3.JAXA宇宙科学研究所、4.九州工業大学)

キーワード：上昇イオンビーム、オーロラ加速域、地磁気活動度、相関分析、電離圏対流

We statistically examine geomagnetic activity dependence of the peak energy and energy flux of H+ and O+ upflowing ion beams in an energy range of 1–25 keV observed by the Arase satellite at high altitudes up to 6 Re geocentric distance. We identified 232 events in which field-aligned beams appeared in either H+ or O+ differential energy flux data obtained by the onboard LEP-i instrument. For the identified beams, we evaluated the correlation coefficient (c.c.) and linear-fitting parameters with the geomagnetic indices (Kp, SYM-H, AE, and PC indices). The H+ beam energy is weakly (c.c. up to ~0.3) proportional to geomagnetic indices except for SYM-H, while the O+ beam energy shows no clear correlation (c.c. less than ~0.1). Although H+ energy flux has little dependence on geomagnetic indices (less than |c.c.|~0.1), the O+ energy flux is proportional to them. In particular, the PC index, which is considered to be a proxy for the intensity of the convection electric field, shows the most significant correlation of ~0.58 when their values were larger than 1 mV/m. This result suggests that the ionospheric frictional heating by enhanced convection predominantly increases the scale height of only O+ ions, supplying denser O+ to the bottom of the auroral acceleration region (~ 3000 km altitude), while H+ ions are constantly abundant at such an altitude regardless of geomagnetic activity.