Predicting surface geomagnetic variations using ionospheric electrodynamic models
Predicting surface geomagnetic variations using ionospheric electrodynamic models
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DOI：
10.1029/2005ja011270
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发表时间：
2005-12
影响因子：
--
通讯作者：
D. Weimer
中科院分区：
文献类型：
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作者：
D. Weimer
[1]描述了一种通过测量行星际磁场（IMF）和太阳风来预测地表地磁变化的技术。该方法使用的双，经验表示的电离层电磁欧拉势的IMF驱动程序的响应。磁势模型最初是为了绘制大尺度场向电流结构而推导出来的，它描述了水平电离层电流的无旋分量，也称为“势流”。使用霍尔和佩德森电导具有固定比率并且不存在电导率梯度的近似，然后从磁势导出霍尔电流。在这种情况下，霍尔电流与无发散的“等效电流”相同，该电流用于导出地表面的地磁变化。如果除了磁势之外还使用电离层电势的经验模型，则避免了电离层电导没有梯度的假设。在该第二方法中，电场提供关于估计的等效电流的方向的附加信息。尽管电导率比近似为固定值，但两种计算方法都能很好地预测大尺度、长周期的地磁变化。包括电场的方法具有稍好的性能，特别是在极冠中。对地下感应电流影响的校正未应用于该演示。这种修正原则上可以改进预测，特别是对影响最大的短周期变化。
[1] A technique is described for predicting ground surface geomagnetic variations from measurements of the approaching interplanetary magnetic field (IMF) and solar wind. The method uses twin, empirical representations of the ionospheric electric and magnetic Euler potentials' response to the IMF drivers. The magnetic potential model, originally derived for mapping the large-scale field-aligned current structure, describes the curl-free component of the horizontal ionospheric current, also called the “potential current.” Using approximations that the Hall and Pedersen conductances have a fixed ratio and that there are no conductivity gradients, then the Hall current is derived from the magnetic potentials. In this case the Hall current is the same as the divergence-free “equivalent current,” which is used to derive the geomagnetic variations at the ground surface. The assumption that the ionospheric conductances have no gradients is avoided if the empirical model for the ionospheric electric potentials is used in addition to the magnetic potentials. In this second method the electric field provides additional information about the direction of the estimated equivalent current. Despite the approximation of a fixed conductance ratio, both calculation methods perform remarkably well for predicting the large-scale and long-period geomagnetic variations. The method that includes the electric fields has a slightly better performance, particularly in the polar cap. Corrections for the effects of currents induced underground were not applied for this demonstration. Such corrections could in principle improve the predictions, particularly for the short-period variations for which the effect is the greatest.