基于协方差矩阵的中国地区1998—2016年地磁急变研究

Study of geomagnetic jerk of China during 1998—2016 based on the covariance matrix

基于43个中国地区地磁台和7个欧洲地区地磁台数据,针对大尺度外源场干扰难以准确估算,通过计算实测值与CHAOS-6模型之间残差的协方差矩阵而从数据中剔除了噪声方向(最大特征值方向)的干扰而获取了干净的长期变化数据,进而分析了1998—2016年期间的中国地区地磁急变.还通过观察三个特征方向的变化而确定外源影响和可能存在的急变.结果表明协方差矩阵方法可以很好地模拟Dst的影响从而降低大尺度的外源干扰,中国和欧洲地区外源场干扰相对于Dst指数的相关性系数分别达到0.791和0.795.中国地区台站对2003.5年和2014年这两个全球急变都有很好的响应,而在2009年前后的急变现象可以认为是一个区域急变事件.两个全球急变在我国的间隔为11年,这反映了我国乃至东亚地区的大尺度地磁场长期变化可能与太阳活动有关.

In order to obtain the clean secular variation data series and the difficulty to estimate the large-scale external field noise,we figured out the covariance matrix of residuals between measurements and field model,CHAOS-6,and get rid of the contribution of the noisy direction(largest eigenvalue)from the 43 Chinese and 7 European observatory’s records.Moreover,we determined the variation of three eigendirections to check the possible jerk during 1998—2016.Results show that the covariance matrix method is capable to excellently approximate the Dstinfluences and remove the large-scale external noise,the correlation coefficients of noise contributions between China and Europe and Dstindex are 0.791 and 0.795 respectively.There are good responses from our results to 2003.5 and 2014’s global jerks.Two jerks around 2009 can be seen as a single regional event.Due to the period between 2003.5 and 2014 is almost 11 years,which implies the big scale geomagnetic secular variation might associate with sun’s activities.