On the formation of a fast thermospheric zonal wind at the magnetic dip equator
On the formation of a fast thermospheric zonal wind at the magnetic dip equator
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DOI：
10.1029/2011gl047255
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发表时间：
2011-05
影响因子：
5.2
通讯作者：
T. Kondo;A. Richmond;H. Liu;J. Lei;S. Watanabe
中科院分区：
文献类型：
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作者：
T. Kondo;A. Richmond;H. Liu;J. Lei;S. Watanabe
利用NCAR热层-电离层-电动力学大气环流模式(TIE-GCM)进行了数值模拟，以了解磁倾角赤道强热层纬向风的成因。模拟结果表明，由于离子阻力的纬度结构，纬向风在磁倾角赤道而不是在地理赤道上刮得很强。在280公里到600公里之间的整个高度都可以看到赤道上的快速风，400公里以上的风主要是通过粘性来加速的。一个无粘性的试验模拟证实，尽管在高海拔的倾角赤道存在离子拖曳最大值而不是相对最小值，但快速赤道风的延伸到400公里以上的高度是通过与低海拔的风的粘性耦合来维持的。基本上，与压力梯度和离子阻力相比，粘度不是很大，但动力学使压力梯度和离子阻力近似平衡，粘度变得重要。模拟结果与DE-2和CHAMP卫星的观测结果一致。因此，我们认为低纬地区的纬向风速受离子阻力和粘性的控制。
Simulations with the NCAR Thermosphere ‐ Ionosphere ‐ Electrodynamics General Circulation Model (TIE‐GCM) have been carried out to understand the cause of strong thermospheric zonal wind at the magnetic dip equator. The simulations show that the zonal winds blow strongly at the magnetic dip equator instead of at the geographic equator due to the latitude structure of ion drag. The fast winds at the dip equator are seen throughout the altitude between 280 km and 600 km, and the wind above 400 km is mainly accelerated via viscosity. A test simulation without viscosity verifies that the extension of the fast equatorial wind to heights above 400 km is maintained by viscous coupling with the winds at lower altitudes, in spite of there being an ion‐drag maximum instead of relative minimum at the dip equator at high altitudes. Basically, viscosity is not so large compared to the pressure gradient and ion drag, but dynamics causes the pressure gradient and ion drag approximately to balance, and viscosity becomes important. The simulation results are consistent with the observations by the DE‐2 and CHAMP satellites. Therefore we suggest that the zonal wind velocity in the low latitude region is controlled by ion drag and viscosity.