高密度极尖区的形成原因

The cusp region is an important window for solar wind particles entering the magnetosphere. Its density is a key parameter for understanding this physical process. Generally, the density of cusp region is about 1~10 cm^-3, but sometimes the satellites can observe cusp density greater than 40 cm^-3, which is called high-density cusp region in this paper. Based on the observations of Cluster satellite from 2001 to 2009, we find 28 high-density cusp crossing events in all the 470 cusp crossing events. We further discuss the favorable conditions of the formation of high-density cusp region, and the external conditions for solar wind efficiently entering cusp region. The results show that the smaller the |MLT-12|, the higher the solar wind density, the existence of low latitude magnetopause reconnection and the positive dipole tilt are favorable conditions for the occurrence of high-density cusp events. When the above-mentioned four conditions are met at the same time, the occurrence rate of high-density cusp events is 100%. The low latitude magnetopause reconnection and large positive dipole tilt are considered as important conditions for the solar wind efficiently entering the cusp region. These results will help us to further understand the physical mechanism of the solar wind entering the cusp region.