利用多卫星观测CIR事件演变的统计分析

Statistical Analysis of Multi-spacecraft Observations on CIR Evolution

根据2007—2009年STEREO-BEHIND(STB)和ACE卫星的行星际磁场和太阳风数据,基于冕洞高速流从太阳向外匀速径向传输假设,讨论了随着STB和ACE卫星与太阳之间的夹角从0°增大至70°时,冕洞发出的高速太阳风形成的相互作用区(CIR)依次扫过STB和ACE卫星的时间差特性,并统计分析了两颗卫星观测到的CIR参数的变化特征.结果显示,可以利用STB对CIR事件的观测来预测这个CIR事件到达ACE的理论时间,时间误差均值和最大值分别为0.217 d和0.952 d,时间误差的产生与STB和ACE卫星观测到的CIR速度大小的不同有关,用速度差异矫正后,时间误差的平均值和最大值可分别减小为0.194 d和0.489 d;STB和ACE卫星观测的CIR事件太阳风速度最大值的线性相关系数达到了0.84,STB和ACE卫星观测到的CIR事件对特征物理量中速度、质子温度的变化最小,而质子密度及总压力的变化最大.分析结果表明,STB和ACE卫星观测到的CIR事件有很强的相似性,STB卫星的CIR,观测可以作为ACE卫星观测CIR事件特征的参考,从而为地球空间环境扰动预报提供依据.

STEREO-BEHIND （STB） and STEREO-AHEAD （STA） drifted behind and ahead of ACE around the Sun, with longitudinal separation increasing day by day. CIR driven by high speed solar wind from coronal holes swept STB, ACE, and STA sequentially. Currently, solar wind observations on ACE are the direct basis for Earth space environment forecasting. Based on interplanetary magnetic field and solar wind observations on STB and ACE, assuming high speed stream transmitted uniformly and radially from coronal holes, characteristics of CIR travel time from STB to ACE with their longitudinal separation increased from 0° to 70° was discussed. Statistical variation char- acteristics of high speed stream parameters were analyzed. The followingwas found out. Firstly, CIRarrival time on ACE could be predicted by CIR observations on STB. The average and maximum errors of travel time was 0.217 d and 0.952 d, respectively. 61% of all events reached ACE earlier than theoretical travel time. The maximum errors of travel time increased with longitudinal separation. The errors of travel time was related to observation differences in CIR speed on STB and ACE. The average and maximum errors of travel time were reduced to 0.194d and 0.489d respectively after being corrected by speed variances. Secondly, linear correlation coefficient of maximum CIR speed on STB and ACE was 0.84. Characteristic parameters of the same CIR on STB and ACE such as speed and proton temperature showed the least difference, while proton density and total pressure showed relatively large difference. The average and maximum range of difference on CIR characteristic parameters observed by STB and ACE, such as maximum speed, maximum proton temperature, maximum total pressure, maximum magnetic field and maximum magnetic southward components, increased with longitudinal separation, while they decreased on maximum proton den- sity. Thirdly, CIR events with larger maximum range and average of observation difference between STB and ACE concentrated in longitude I0~, 25~ and 47~, corresponding to CR2059-2060, CR2065- 2066, CR2077-2078, which had larger errors on travel time. These results showed that there was a strong similarity between CIR observations on STB and ACE. Therefore, CIR observations on STB could be used as reference of CIR characteristics on ACE, and provided basis for forecasting of Earth space environment disturbance.