福衛三號全電子濃度對於太陽風造成中等尺度磁場擾動的增加反應; COSMIC Observations of TEC Enhancements in Response to moderate disturbances in the solar wind

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题名:	福衛三號全電子濃度對於太陽風造成中等尺度磁場擾動的增加反應;COSMIC Observations of TEC Enhancements in Response to moderate disturbances in the solar wind
作者:	賴珮晨;Pei-Chen Lai
贡献者:	太空科學研究所
关键词:	電場;全電子濃度;福衛三號;COSMIC;TEC;penetration electric field
日期:	2011-07-22
上传时间:	2012-01-05 14:11:10 (UTC+8)
摘要:	本論文主要在於研究全電子濃度 (TEC, Total Electron Content) 在高速太陽風(HHS, high speed stream) 經過地球時的變化情形. 我們分析的資料以COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) 衛星觀測資料為主, 發生時間是2007年11月18-22日為期五天. 發生在SSH之前的共轉反應區 (CIR, Corotating Interaction Region) 期間內, 被擠壓的電漿濃度有明顯的升高, 伴隨的行星際磁場 (IMF, Interplanetary Magnetic Field) 對地球造成中等尺度磁暴的影響. 我們利用垂直高度的積分算出在每個掩星路徑正切點的TEC後, 發現在當地時間中午左右時中高緯度的TEC有增值的現象, 同時IMF的狀態是一個完整磁暴週期中的主要相位 (main phase). 分析資料的結果亦顯示某些TEC增值後的數字是電離層安靜期的3到4倍. 為了尋求增值的原因, 我們使用Hardy極區能量模型作為依據. 在類似的太空環境條件下, Hardy極區能量模型指出從磁層注入電離層高緯度地區的能量不是主要讓TEC增加的原因. 因此我們認為COSMIC白天觀測到的電漿濃度增高的情形是由其他地區的轉移 (transport) 來的. 從ACE衛星量測到的太空資料可以讓我們估計從磁層到電離層的穿透電場 (penetration electric field) 強度, 由此可以得到其與地磁場作用後的漂移速度 (E_B drift velocity). 最後我們亦使用TIEGCM的模擬結果來作比較. COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) satellite data, acquired during five days in November 2007, were analyzed to study the Total Electron Content (TEC) enhancements as a high speed stream (HSS) in the solar wind passed the Earth. In the case of Julian Day 322-326, the HSS arrival was closely preceded by the arrival at the first Lagrange point L1 of an interplanetary coronal mass ejection (ICME). The corotating interaction region (CIR) at the leading edge of the HSS was marked by a sharp increase in plasma density, followed by an intensification and rotation of the interplanetary magnetic field (IMF), inducing a moderate magnetic storm. We calculated the TEC by integrating electron density profiles over altitude and assigned values to the locations of ray-tangent points. The TEC enhancements appeared at mid- to high-magnetic latitudes during the main phase of a magnetic storm driven by the fast stream’s leading edge. Some TEC increases exceeded quiet-time values by a factor of 3 to 4. The Hardy model for distributions of auroral electron precipitation indicated that no source for new plasma creation was present in the range of magnetic latitudes where the TEC enhancements occurred. Thus, the TEC enhancements must reflect transport effects. Neutral winds generated at auroral latitudes should push dayside plasma equatorward, just as opposite to the COSMIC observations. Rather, required transport implies plasma drifts from low to higher latitudes, due to the dawn-to-dusk penetration electric fields. ACE measurements allow estimates of penetration electric field strengths. These are then mapped to the ionosphere and used to calculate plasma transport velocities. We compare empirical solutions of the continuity equation with the TIEGCM predictions.
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