In this paper, we have evaluated the role of interplanetary magnetic field (IMF) By on the asymmetry of the ring current during the main phase of geomagnetic storms. The mean H variations have been calculated using 31 ground magnetic stations over magnetic latitudes of 09–45° following the methodology of Li et al. (2011, https://doi.org/10.1029/2011JA016886). Further, the magnetic local time (MLT) variations in the H component at these stations w.r.t. the mean H were investigated for three cases of geomagnetic storms with varying southward IMF Bz and IMF By conditions. Significant ring current asymmetries were observed during the main phase of geomagnetic storms. The primary role of IMF Bz on the asymmetry of the ring current is observed from these cases. More importantly, the investigation brings out for the first time, the additional role of IMF By in influencing the MLT distribution of ring current observed at ground magnetic stations. Under southward IMF Bz conditions, it is shown based on SuperDARN and AMPERE data that IMF By can alter the MLT distribution of ring current under suitable conditions. The timescales of IMF By also play very important role in determining the asymmetry in the ring current. Under steady convection state, IMF By can rotate the convection cells based on its polarity, which in turn can change the MLT distribution of ring current observed by low‐latitude ground stations. This investigation, thus, brings out the important role of IMF By on the asymmetric MLT distribution of ring current under southward IMF Bz.

中文翻译：

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地磁台站观测到的IMF by对南向IMF Bz条件下环电流不对称的影响：案例研究

在本文中，我们通过在地磁风暴主相期间环形电流的不对称性来评估行星际磁场（IMF）的作用。根据Li等人的方法，使用31个地磁站在09-45°的纬度上计算了平均H变化。（2011，https://doi.org/10.1029/2011JA016886）。此外，这些站的H分量中的磁局部时间（MLT）变化与平均H调查了三例情况不同的南向IMF Bz和IMF By条件的地磁风暴。在地磁风暴的主要阶段观测到明显的环流不对称性。从这些情况中可以看出，IMF Bz在振铃电流不对称方面的主要作用。更重要的是，这项调查首次揭示了IMF通过影响地面磁站观测到的环形电流的MLT分布而发挥的额外作用。在IMF Bz向南的条件下，根据SuperDARN和AMPERE数据显示，IMF By可以在合适的条件下改变环形电流的MLT分布。IMF By的时标在确定振铃电流中的不对称性方面也起着非常重要的作用。在稳定对流状态下，IMF By可以根据其极性旋转对流单元，这反过来可以改变低纬度地面站观测到的环形电流的MLT分布。因此，这项研究通过在IMF Bz向南的环流的非对称MLT分布上发挥了IMF的重要作用。