地磁扰动的时空变化规律和产生原因:统计和模拟研究

On the spatio-temporal variations and causes of geomagnetic perturbations

地磁感应电流(Geomagnetically Induced Currents, GICs)是发生在地球表面的一种空间天气现象,对石油管道、电缆等长距离地面基础设施会产生不利影响.研究GICs的产生原因及其与太阳风驱动条件的关系对于预报灾害性空间天气具有重要意义.由于GICs的产生与地磁场扰动紧密相关,本文利用北半球100多个地磁台站的长期监测数据,统计分析了地磁扰动及其时间变化率(磁扰率)与各种太阳风参数/地磁指数之间的相关性,并以2013年3月17日的磁暴事件为例,采用全球空间天气模型框架(space weather modeling framework, SWMF)模拟了磁暴期间地磁场扰动在北半球的分布以及日地空间中各电流体系对地磁扰动的作用.研究结果表明:(1)中低纬度的地磁扰动北向分量Bx与表征环电流强度的SYM-H指数呈现较高的正相关性(相关系数CC=0.75),高于它与亚暴AE指数以及其他太阳风参数的相关性,说明磁暴期间环电流是导致中低纬度北向磁场减弱的主因,而在平静期间东向的磁层顶电流是中低纬度北向磁场增强的原因;(2)地磁扰动率与太阳风动压、行星际磁场IMF Bz、亚暴AE指数或者磁暴SYM-H指数均没有强相关性;(3)高纬地区的磁扰率通常大于低纬地区,而较强的磁扰率倾向于出现在中等磁暴或者中等-强亚暴期间的中高纬地区;(4)SWMF模型能较好地反演地磁平静时的北向地磁扰动和磁暴时的东向地磁扰动;(5)磁暴期间,磁层电流对中低纬度北向地磁扰动的贡献最大,而电离层霍尔电流对高纬地区的北向地磁扰动有着很强的支配地位;另外,高纬地区的东向地磁扰动主要由霍尔电流控制,而中低纬地区则受制于场向电流.

Geomagnetically Induced Currents(GICs)is one important space weather phenomenon that occurs on the Earth surface which can adversely affect long-distance ground infrastructures such as oil pipelines and power cables.It is of great significance to study the causes of GIC and its relationship with solar wind conditions for the prediction of catastrophic space weather.Since GICs are closely related to geomagnetic perturbations,this paper uses long-term monitoring data from more than 100 geomagnetic ground stations in the Northern Hemisphere to statistically analyze the correlation between various solar wind parameters/geomagnetic indices and the geomagnetic perturbations as well as their time variations.Furthermore,using Space Weather Model Framework(SWMF),we simulate the distribution of geomagnetic disturbances in the Northern Hemisphere during the March 17,2013 storm to understand the effects of various current systems on geomagnetic perturbations.The results show that:(1)The northward component of the geomagnetic perturbation Bx during storm is highly correlated(CC=0.75)with the SYM-H index which represents the intensity of ring current;the correlation is higher than that with the AE index and other solar wind parameters,indicating that the ring current is the main cause of the weakening of the northward magnetic field at middle and low latitudes;On the other hand,the eastward magnetopause current during quiet periods is the reason for the enhancement of the northward magnetic field at middle and low latitudes.(2)No strong correlation is found between the time variations of magnetic perturbations and solar wind flow pressure,interplanetary magnetic field Bz,substorm index AE,or geomagnetic storm index SYM-H.(3)The time variations of the magnetic perturbations at high latitudes is usually larger than that at lower latitudes,and such strong variations tend to occur during moderate storms or moderate/strong substorms.(4)SWMF model can capture northward geomagnetic perturbations during quiet time and eastward perturbations during storm time in general.(5)During magnetic storms,magnetosphere currents contribute most to the northward geomagnetic perturbations at middle and low latitudes,while at high latitudes the Hall current in the ionosphere is the dominant contributor.In addition,the eastern geomagnetic perturbations at high latitudes are mainly controlled by the Hall current,while that at middle and low latitudes are determined by field-aligned currents.