【摘要】 近年来多种观测表明夜间中纬电离层存在电离密度峰值，但是夜间中纬电离峰(Mid-latitudinal Ionization Peak, MIP)结构的形成机制尚不完善.利用Swarm-A卫星观测数据，本文首先统计了地磁平静期分季夜间中低纬电离层电离密度的空间分布，结果表明夜间MIP结构在低太阳活动强度和午夜后最显著，主要出现在磁纬±40°附近.然后，本文首次使用SAMI2模型成功重现了低太阳活动强度春分日地磁平静期夜间MIP结构，模拟结果表明MIP结构在午夜后和顶部电离层-等离子体层最显著.通过重构SAMI2模型中电离层电离密度连续性方程的计算揭示了各种物理过程对于450 km高度顶部电离层夜间MIP结构的贡献.日落前后东太平洋扇区率先形成南半球MIP结构，中纬电离层较长时间的光电离、东向磁偏角导致的赤道向中性风和较弱的PRE电场均有利于其形成.深夜MIP结构的形成机制主要是西向纬向电场导致的向内E×B漂移，通过快速降低低纬电离层电离密度形成MIP结构.模拟结果还表明中性风对于夜间MIP结构的贡献取决于其等效垂直风的地方时-纬度分布.更多还原

【Abstract】 Recent observations have shown that there is an ionization density peak in the nighttime mid-latitudinal ionosphere, but the formation mechanism of the nighttime mid-latitudinal ionization peak(MIP) structure is not perfect. Using Swarm-A satellite observation data, this paper firstly counts the spatial distribution of the ionization density in the nighttime mid-and low-latitudinal ionosphere on the equinox months under the geomagnetic quiet activity, and the results show that the nighttime MIP structure is most prominent after midnight and under low solar activity, which mainly occurs around the magnetic latitude ±40°. Then, for the first time, using SAMI2 model, we successfully reproduced the nighttime MIP structure on spring equinox under low solar activity and geomagnetic quiet activity. Simulation shows that the MIP structure is most prominent after midnight and at topside ionosphere-plasmasphere. The reconstruction of the ionosphere ionization density continuity equation of SAMI2 model reveals the contribution of various physical processes for the nighttime MIP structure of 450 km height topside ionosphere. Before and after sunset, the eastern Pacific sector ionosphere firstly formed the MIP structure in the southern hemisphere, and the long-lasting sunlight at the mid-latitudinal ionosphere, the equatorward neutral wind induced by the eastward magnetic declination and the weaker PRE electric field are all conducive to its formation. The formation mechanism of late-night MIP structure is mainly the inward E×B drift induced by the westward zonal electric field, which forms the MIP structure by rapidly reducing the ionization density of the low-latitudinal ionosphere. The simulation results also show that the contribution of the neutral wind to the nighttime MIP structure depends on the local time-latitudinal distribution of its effecftive vertical wind.更多还原