Direct determination of IMF BY‐related cusp current systems, using SuperDARN radar and multiple ground magnetometer data: A link to theory on cusp current origin
Direct determination of IMF BY‐related cusp current systems, using SuperDARN radar and multiple ground magnetometer data: A link to theory on cusp current origin
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使用 SuperDARN 雷达和多个地面磁力计数据直接确定 IMF BY 相关尖点电流系统：尖点电流起源理论的链接
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
T. Moretto
中科院分区：
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作者：
O. Amm;M. Engebretson;R. Greenwald;H. Lühr;T. Moretto
我们分析了电离层“增强对流事件”的尖点1996年11月13日，在1900 UT，通过使用数据的SuperDARN雷达，和IMAGE，格陵兰岛，MACCS和CANOPUS磁强计阵列，并从其他磁强计站。该事件发生在IMF BY分量从正到负的转变以及电离层电势模式的相关重新配置之后的20分钟。这些数据允许在电离层电场和地面磁场方面对事件进行瞬时二维视图。“特征线法”被用来获得所研究的时间间隔的电离层电导、实际电离层电流和场向电流的分布。我们的研究结果表明，该地区的雷达观测到的对流增强与低电导率的区域，范围仅略高于紫外线电导值。然而，由于强烈增强的电场，它产生了增强的向西向流动的霍尔和南向流动的彼得森电流。在对流增强区的北方和南部边界，分别观察到向下和向上的FACs片，其量级约为0.5 A/km 2。电流系统的几何形状类似于DPY电流系统[Friis-Christensen and Wilhjelm，1975]。使用我们的研究结果，我们测试的替代理论尖电流的起源，导致不同的预测尖电流系统的相对位置相对于开闭场线边界。该边界的位置是根据DMSP F10卫星数据推断的。我们得到的电流系统的中心明显位于开闭磁力线边界的极向，因此支持Lee等人[1985]的观点，即尖点FAC是由磁层顶磁场的旋转不连续性引起的。与此相反，克劳尔和班克斯[1986年]的想法，即太阳风Ez分量到电离层的映射是导致尖点电流系统的原因，这一想法不被支持。
We analyze an ionospheric “enhanced convection event” in the cusp on November 13, 1996, at 1900 UT, by using data of the SuperDARN radar, and of the IMAGE, Greenland, MACCS and CANOPUS magnetometer arrays; and from other magnetometer stations. The event occurs ∼20 minutes after a transition of the IMF BY component from positive to negative and an associated reconfiguration of the ionospheric electric potential pattern. The data allow an instantaneous two-dimensional view of the event in terms of the ionospheric electric and ground magnetic field. The “method of characteristics” is used to obtain distributions of ionospheric conductances, actual ionospheric currents, and field-aligned currents (FACs) for the interval under study. Our results show that the region of enhanced convection observed by the radar is associated with a region of low conductances, ranging only slightly above the UV conductance values. However, owing to the strongly enhanced electric field, it produces enhanced westward flowing Hall and southward flowing Pedersen currents. At the northern and southern borders of the enhanced convection region, sheets of downward and upward FACs are observed, respectively, with magnitudes of around 0.5 A/km2. The geometry of the current system resembles a DPY current system [Friis-Christensen and Wilhjelm, 1975]. Using our results, we test alternative theories on cusp current origin that lead to different predictions of the relative location of the cusp current system with respect to the open-closed field line boundary. The location of this boundary is inferred from DMSP F10 satellite data. The center of our resulting current system is located clearly poleward of the open-closed field line boundary, thus favoring the idea of Lee et al. [1985] that the cusp FACs are caused by a rotational discontinuity of the magnetic field at the magnetopause. In contrast, the idea of Clauer and Banks [1986] that a mapping of the solar wind Ez component to the ionosphere is responsible for the cusp current system is not supported.