Electromagnetic Energy Transfer across the Magnetopause
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摘要: 利用全球磁流体力学（MHD）模拟结果，通过确立包含磁层顶的太阳风流线内边界来识别三维磁层顶位形，并以极尖区位置作为磁层顶日侧与夜侧的分界线，在此基础上定量研究了不同条件下穿过磁层顶向磁层内输入的电磁能量. 研究发现，磁层顶的能量传输与太阳风条件密切相关，磁重联是控制电磁能量传输的重要机制. 结果表明，当IMF（行星际磁场）南向时，极尖区后方的磁尾附近存在电磁能输入最大值，当IMF北向时，电磁能输入最大值发生在极尖区附近；南向IMF条件下，在IMF强度增大或太阳风密度增大时，磁层顶电磁能传输的电磁能量比北向IMF条件时增加更显著. 太阳风通过调节磁层顶面积间接影响到磁层顶能量传输大小. 研究还发现，北向IMF与南向IMF条件下穿过磁层顶的电磁能输入的比值范围约为10%～30%，此比值一定程度上反映了北、南方向IMF与地磁场磁重联效率的比值.Abstract: A three-dimensional adaptive magnetohydrodynamic (MHD) model is used to examine the electromagnetic energy flow from the solar wind to the magnetosphere. The magnetopause is determined by finding approximately the inner edge of the void encompassed by the solar wind stream lines, and the magnetopause is divided into nightside and dayside part by polar cusp region. This study found that the magnetopause energy transfer has close relations with solar wind conditions. The magnetopause area also effects energy transfer. For northward IMF, most of the electromagnetic energy flux inflow occurs near the polar cusps on magnetopause; for southward IMF the largest electromagnetic energy input into the magnetosphere occurs at the tail lobe behind the cusps. Under southward IMF conditions, more electromagnetic energy input can be identified as increasing solar wind density while it does not enhance as much for northward IMF. Our results suggest that the mechanisms proposed to electromagnetic energy transfer are mainly due to reconnection. If the electromagnetic energy coupling between the solar wind and the magnetosphere can be interpreted as a proxy for the reconnection efficiency, the efficiency during northward IMF is about 10%～30% of that for southward IMF under the solar wind conditions we considered.
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Key words:
- Magnetopause /
- Energy transfer /
- Reconnection /
- MHD simulation
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