Sq电流引起的大地电磁响应函数变化
Variations in magnetotelluric response functions caused by Sq currents
摘要：
大地电磁（MT）响应受空间非均匀源场的影响。最近，甚至在局部源电流很少流动的中纬度地区也报告了这种偏差。这项研究的重点是在MT响应的变化所产生的太阳安静（Sq）电流的焦点纬度。通过改变Sq电流的中心来计算60 s时的MT响应。聚焦纬度的轻微变化会引起视电阻率和相位的大偏移。在平静的地磁活动期间，中心在20-45 N的范围内变化，而当有干扰时，这个范围会缩小。即使这项研究认为只有一个有限的情况下，结果表明，在平静的地磁活动和MT响应与地磁活动的幅度的相关性期间的阻抗的不稳定性。因此，即使台站位于中纬度，也需要仔细处理延时MT探测的阻抗，例如，检查电离层电流状况及其对地磁活动的依赖性。
英文摘要：
The magnetotelluric (MT) responses of the Earth are biased by spatially heterogeneous source fields. Recently, such biases have been reported even in mid-latitude areas, where localized source currents rarely flow. This study focuses on shifts in the MT responses arising from variations in the focus latitude of the solar quiet (Sq) current. The MT responses at 60 s were calculated by changing the center of the Sq current. Slight variations in the focus latitude cause large shifts in the apparent resistivity and phase. During periods of quiet geomagnetic activity, the center varies within a wide range of 20-45 N, whereas this range narrows when there are disruptions. Even though this study considers only a limited case, the results demonstrate the instability of the impedances in periods of quiet geomagnetic activity and a correlation of the MT responses with the magnitude of the geomagnetic activity. As a consequence, even when a station is located at mid-latitudes, the impedances need to be treated carefully for time-lapse MT soundings, for example, by checking the ionospheric current conditions and their dependence on the geomagnetic activity.
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