結合實地觀測和STEREOHI圖像觀測分析

劉四清+王晶晶+陳艷紅

摘 要：基于單顆STEREO衛星日球層成像儀（Heliospheric Imager，HI）圖像的固定Φ角擬合法（Fixed-Φ，FΦ）和調和均值擬合法（Harmonic-mean，HM），結合STEREO和ACE衛星的太陽風實地觀測數據，深入分析了2010年15個日冕物質拋射（CME）事件，對比討論了這兩種方法在提取CME參數如太陽赤道平面的主傳播方向、傳播速度的效果，其中FΦ擬合法假設CME是固定方向傳播的小質點，HM擬合法假設CME為具有球形前沿的通量繩結構，結果發現：（1）使用HM擬合法分析得到的CME主傳播方向與太陽-實地觀測點的夾角平均值是9.5°，小于FΦ擬合法的19.7°；（2）HM擬合法分析的預計到達時間與實測ICME起始時間的平均誤差和最大誤差分別為0.282 d和0.805 d，明顯小于FΦ擬合法。該文也使用結合STEREO兩顆衛星HI圖像的直接三角法（Direct-triangulation，DT）和球面切線法（Tangent-to-a-sphere，TS），深入分析了5個朝向地球的CME事件，其中，DT和FΦ擬合法的假設相同，TS和HM擬合法的假設相同，結果發現：（1）這兩種方法分析的CME主傳播方向與日地連線的夾角最大值分別是13.2°和21.1°，明顯小于單顆衛星觀測的20.7°和27.5°；（2）其中4個CME事件使用方法得到的線性擬合加速度不超過0.4 m/s2，這說明CME在主傳播方向上的速度變化在1 AU內不超過100 km/s；（3）使用TS方法得到的預計到達時間與實測ICME起始時間的絕對誤差最小，平均值和最大值分別是2.3 hr和5.8 hr。可見，利用HI圖像提取CME傳播參數時，加入CME前沿結構假設和結合多角度觀測都能夠有效地減小擬合誤差。

關鍵詞：日冕物質拋射 STEREO HI

Abstract：Characteristic parameters of 15 CMEs in 2010， such as direction of propagation and transit speed in Solar equatorial plane， were analyzed by Fixed-Φ（FΦ） and Harmonic-mean（HM） approximation based on Heliospheric Imager （HI） observations from one spacecraft， combined with in-situ observations of solar wind on STEREO and ACE. CME was modeled as a small element with a fixed direction of propagation in FΦ approximation. HM approximation assumed CME could be modeled as a flux-rope， whose circular front anchored at the Sun and center propagated on a fixed direction of propagation. We found that： （1）Average value of separation angle between CME propagation direction and Sun-spacecraft line obtained by FΦ and HM approximation was 19.7° and 9.5°， respectively. （2）Average and maximum of differences between predicted arrival time and in-situ ICME start time was 0.282 and 0.805 day， respectively. Characteristic parameters of 5 CMEs which propagated toward the Earth were analyzed by Direct-triangulation （DT） and Tangent-to-a-sphere （TS） method based on HI observations from both STEREO spacecraft. DT and TS method could be done under the same assumption of FΦ and HM approximation， respectively. We found that： （1）Maximum value of separation angle between CME propagation direction and Sun-Earth line by these two methods was 13.2° and 21.1°， respectively， which was less than that obtained from one spacecraft significantly. （2）Linear accelerations and transit speed change obtained by TS method of 4 CMEs was no more than 0.4 m/s2 and 100 km/s， respectively. （3）Average and maximum of differences between in-situ ICME start time and predicted arrival time obtained by TS method was 2.3 hr and 5.8 hr， respectively， which was less than that obtained from other methods. In summary， differences between CME characteristic parameters obtained from HI observations and in-situ observations could be effectively reduced by modeling CME as a flux rope as well as combining with multi-point HI observations.

Key Words：CME； STEREO； HI

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