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The distribution of the ring current: Cluster observations

【标题】The distribution of the ring current: Cluster observations

【Title】The distribution of the ring current: Cluster observations

【DOI】10.5194/angeo-29-1655-2011

【作者】 张清和; Y. Kamide; 刘瑞源; 杨惠根; 胡红桥; 张北辰; 刘顺林

【Author】 Zhang Qinghe ; Y. Kamide ; Liu Ruiyuan ; Yang Huigen ; Hu Hongqiao ; Zhang Beichen ; Liu Shunlin

【期刊】Annales Geophysicae

【Journal】Annales Geophysicae

【期刊年份】2011

【卷】29

【期】

【关键词】 磁层物理

【Keywords】 Magnetospheric physics (Current systems; Magnetospheric configuration and dynamics)

【摘要】Extending previous studies, a full-circle investigation of the ring current has been made using Cluster 4-spacecraft observations near perigee, at times when the Cluster array had relatively small separations and nearly regular tetrahedral configurations, and when the Dst index was greater than -30 nT (non-storm conditions). These observations result in direct estimations of the near equatorial current density at all magnetic local times (MLT) for the first time and with sufficient accuracy, for the following observations. The results confirm that the ring current flows westward and show that the in situ average measured current density (sampled in the radial range accessed by Cluster similar to 4-4.5 R(E)) is asymmetric in MLT, ranging from 9 to 27 nA m(-2). The direction of current is shown to be very well ordered for the whole range of MLT. Both of these results are in line with previous studies on partial ring extent. The magnitude of the current density, however, reveals a distinct asymmetry: growing from 10 to 27 nA m(-2) as azimuth reduces from about 12:00 MLT to 03:00 and falling from 20 to 10 nA m(-2) less steadily as azimuth reduces from 24:00 to 12:00 MLT. This result has not been reported before and we suggest it could reflect a number of effects. Firstly, we argue it is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00 MLT and downward out of the ring current around 14:00 MLT. Secondly, we note that it is also consistent with a possible asymmetry in the radial distribution profile of current density (resulting in higher peak at similar to 4-4.5 R(E)). We note that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT).

【Abstract】Extending previous studies, a full-circle investigation of the ring current has been made using Cluster 4-spacecraft observations near perigee, at times when the Cluster array had relatively small separations and nearly regular tetrahedral configurations, and when the Dst index was greater than -30 nT (non-storm conditions). These observations result in direct estimations of the near equatorial current density at all magnetic local times (MLT) for the first time and with sufficient accuracy, for the following observations. The results confirm that the ring current flows westward and show that the in situ average measured current density (sampled in the radial range accessed by Cluster similar to 4-4.5 R(E)) is asymmetric in MLT, ranging from 9 to 27 nA m(-2). The direction of current is shown to be very well ordered for the whole range of MLT. Both of these results are in line with previous studies on partial ring extent. The magnitude of the current density, however, reveals a distinct asymmetry: growing from 10 to 27 nA m(-2) as azimuth reduces from about 12:00 MLT to 03:00 and falling from 20 to 10 nA m(-2) less steadily as azimuth reduces from 24:00 to 12:00 MLT. This result has not been reported before and we suggest it could reflect a number of effects. Firstly, we argue it is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00 MLT and downward out of the ring current around 14:00 MLT. Secondly, we note that it is also consistent with a possible asymmetry in the radial distribution profile of current density (resulting in higher peak at similar to 4-4.5 R(E)). We note that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT).

【基金/项目】 国家自然科学基金项目(11ZR1441200) ; 海洋公益性行业科研专项经费项目 (201005017) ; 极区电离层对日侧磁重联的响应研究 ; 极区能量沉积过程及其对120E子午面电离层影响的研究 ; 日侧冕状极光的分类及其产生机制研究 ; 极区电离层南北极对比研究 ; 极区海洋大气与空间环境业务化监测及其在气候变化预测中的应用(地球极区太阳风能量注入过程与模式)

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