Solar Wind/IMF Influences on Field-Aligned Electrons in Earth’s Polar Region

In Earth’s polar regions, Field-Aligned Electrons (FAEs) have been studied for decades. However, their response to solar wind and IMF conditions still require further investigation. In this study, we used Cluster observation data to examine the influence of solar wind and IMF on polar region FAEs. The FAE event was selected based on an electron flux threshold exceeding 3×10⁸ cm^-2s^-1 for analysis. Several notable findings were obtained. (1) FAE occurrence rates increase with solar wind dynamic pressure (Psw) increasing for both upward and downward FAEs. In the northern hemisphere, however, the occurrence rates appear to rise more sharply than in the southern hemisphere. (2) The distribution of FAE occurrence shows two peaks in relation to IMF By: a major peak around IMF By = -20 nT and a minor peak around IMF By = +20 nT. (3) FAEs occur most frequently when IMF Bz>0 and IMF By>0, which corresponds to an IMF clock angle between 12:00 and 03:00. (4) Since  geomagnetic activity is driven by solar wind–magnetosphere interaction, we also examined FAE occurrence in relation to the geomagnetic activity Kp and AE indices. The results indicate that FAE occurrence depends primarily on increasing AE activity. We discuss potential mechanism underlying these results. Variation in FAE occurrence appears to be largely controlled by magnetospheric configuration and its response to solar wind conditions. Further analysis suggests that FAE are closely associated with FAC in polar space. It is significant to understand the physical process in the polar region.