[P-EM12] 太陽地球系結合過程の研究基盤形成

[PEM12-16] What can we learn from the quiet high-latitude ionosphere?

*大山 伸一郎^1,2,3、バンハマキ, ヘイキ³、ツァィ, レイ³、アイキオ, アニータ³、リートベルト, マイク⁴、小川 泰信²、ライタ, テロ⁵、ケリンサルミ, ミリヤム⁶、カウリスティ, キルスティ⁶、コゼロフ, ボリス⁷、新堀 淳樹¹、塩川 和夫¹、津田 卓雄⁸、坂野井 健⁹ (1.名古屋大学宇宙地球環境研究所、2.国立極地研究所、3.オウル大学、4.EISCAT科学協会、5.オウル大学ソダンキラ地球物理観測所、6.フィンランド気象研究所、7.ロシア極域地球物理研究所、8.電気通信大学、9.東北大学)

キーワード：電離圏、熱圏、高緯度、オーロラ

The auroral oval never disappears even for periods of very low geomagnetic activity. This suggests that magnetospheric energies would be more or less supplied to the polar region and cause corresponding disturbances in the ionosphere and thermosphere. The impacts on the upper atmosphere are likely insignificant to modulate in a global scale but quiet-time measurements may give a new insight to investigate mechanisms working in the M-I-T coupled system, which might be masked by many concurring processes during geomagnetically disturbed periods. This study focuses on a couple of features during period of geomagnetically quiet condition with a weak but significant auroral enhancement at relatively high latitudes. One is an ephemeral red arc, which would represent a moment of the stable auroral red (SAR) arc birth coinciding with pseudo breakup. This is the first time ever to capture the moment because initial phase of the typical SAR arc tends to be masked by bright aurorae at the substorm expansion phase. Two is negative U.V in the F-region measurement. The thermospheric wind (U) flows after the ionospheric ion velocity (V), and in most cases, U is approximately parallel to V, i.e., positive U.V. This is evidence of kinetic energy conversion from ions to neutral particles. However, U.V can be negative when V suddenly changes direction but U delays due to its inertia. A negative U.V results in larger Joule heating than the positive U.V case. This presentation will conclude importance of studying geomagnetically quiet condition to figure out fundamental mechanisms, which cause disturbances in the ionosphere and thermosphere also during active periods.