弱尾活动和强尾活动的不对称叶瓣对流观测
Observations of Asymmetric Lobe Convection for Weak and Strong Tail Activity
摘要：
在这项研究中，我们使用来自星团上电子漂移仪的高质量对流数据来研究当行星际磁场具有主导的东西向（B $_{y}$）分量时，近地尾巴活动如何影响磁尾叶的平均对流模式。两个不同的代理已被用来代表不同程度的重连在近地尾巴：AL指数的值和亚暴阶段确定的亚暴开始和阶段从指数的Electrojet算法。我们发现，对流的变化，从占主导地位的Y $_{GSM}$方向，但相反的两个半球，更倾向于向等离子体片的流动，作为对流的南北分量增加时，重联增强在近地尾巴。这一结果与最近对电离层对流的观测结果一致，这表明当尾部重连增加时，夜侧对流模式变得更加南北对称。这也得到了来自两半球的同步极光观测的支持，这表明共轭极光特征在亚暴扩展阶段变得更加对称。不对称性的减少意味着在近地尾强重联期间，叶中的不对称压力平衡发生了变化。
英文摘要：
In this study we use high-quality convection data from the Electron Drift Instrument on board Cluster to investigate how near-Earth tail activity affects the average convection pattern in the magnetotail lobes when the interplanetary magnetic field has a dominating east-west (B$_{y}$) component. Two different proxies have been used to represent different levels of reconnection in the near-Earth tail: The value of the AL index and the substorm phases identified by the Substorm Onsets and Phases from Indices of the Electrojet algorithm. We find that the convection changes from a dominantly Y$_{GSM}$direction, but opposite in the two hemispheres, to a flow oriented more toward the plasma sheet, as the north-south component of the convection increases when reconnection enhances in the near Earth tail. This result is consistent with recent observations of the convection in the ionosphere, which suggest that the nightside convection pattern becomes more north-south symmetric when tail reconnection increases. This is also supported by simultaneous auroral observations from the two hemispheres, which shows that conjugate auroral features become more symmetric during substorm expansion phase. The reduced asymmetry implies that the asymmetric pressure balance in the lobes is altered during periods with strong reconnection in the near-Earth tail.
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