太陽磁暴期間由地磁場導引電流感應的地面電場模擬

Abstract

太空天氣在磁層和電離層的日變化中起著重要作用，從而影響大氣層內及地表的人類活動。太陽風攜帶星際磁場驅動空間中的地磁場導引電流，進而在地球表面產生地磁感應電場和地磁感應電流。地磁感應電流可能會損壞電網中的變壓器和傳輸線、鐵路設備、通信電纜以及管道網絡。文獻中通常將地表的地磁感應電場起源簡化為面電流或線電流。在本研究中，將探討地球表面的地磁感應電場與磁暴期間地磁場導引電流之間的關係。通過磁流體力學模型模擬地球磁暴期間磁層對太陽風的響應，並將該響應作為邊界條件，進一步模擬電離層的響應。最後，應用時域有限差分法計算基於電離層響應推導出的電流源，並 獲得地磁感應電場的時空分佈。本研究模擬了 2017 年 5 月磁暴、萬聖節磁暴以及卡靈頓事件三種情境下的地磁感應電場分佈，以評估太陽風暴可能帶來的災害。此外，模擬中還揭示了類似范艾倫輻射帶的現象。

Space weather plays an important role in the diurnal variation of magnetosphere and ionossphere, hence impacts the human activities in the atmosphere and on the ground. The solar wind accompanied by the interplanetary magnetic field (IMF) drives field-aligned cur rents (FACs) in space, which in turn drive geomagnetically induced electric field (GIE) and geomagnetically induced current (GIC) on the Earth surface. The GIC may damage trans formers and transmission lines in power grids, railway equipment, communication cables and pipeline networks. The ground-level GIE was assumed to originate from some simpli fied current sheet or line current in the literature. In this work, the relationship between GIE on the Earth surface and the FACs during a magnetic storm will be studied. The magnetospheric response to the solar wind during geomagnetic storms is simulated by using an MHD model. The ionospheric response is then simulated by taking the magnetospheric response as the boundary conditions. Finally, an FDTD method is applied to compute the spatial and temporal distributions of GIE in terms of the current sources derived from the ionospheric response. The distributions of GIE are simulated in three scenarios of May 2017 storm, Halloween storm and Carrington storm, respectively, to evaluate possible hazards of solar storms. In addition, phenomena akin to the Van Allen radiation belts are revealed in the simulations.