Statistical Study of Hot Flow Anomaly Induced Ground Magnetic Ultra‐Low Frequency Oscillations

Abstract

AbstractPc5 ULF waves play an important role in transporting energy and particles in the coupled magnetospheric and ionospheric system. They are known to be initiated by dynamic pressure fluctuations upstream of the magnetopause, including those induced by hot flow anomalies (HFAs). However, the role of HFAs in generating magnetospheric and ground magnetic Pc5 ULF oscillations has not been investigated statistically yet. Thus, in this paper, we investigate the contribution of HFAs to ground magnetic Pc5 ULF oscillations and analyze how the characteristics of HFAs influence these oscillations, based on the coordinated observations between the THEMIS probes and the ground magnetometers at high latitudes during the years 2008, 2009 and 2019. We find that HFAs can serve as a notable source of ground magnetic Pc5 ULF oscillations, with about 18.9% of Interplanetary Magnetic Field (IMF) discontinuity‐induced HFAs associated with discernible enhancements in Pc5 ULF wave power, whereas spontaneous HFAs play a comparatively minor role in generating these oscillations. Furthermore, we observe that the cores of HFAs are likely to contribute more significantly to modulating the induced ground magnetic Pc5 ULF oscillations than their compressed boundaries. More dynamic pressure reductions within HFA cores correspond to stronger ground magnetic Pc5 ULF oscillations. Additionally, HFAs can propagate with the IMF discontinuity along the bow shock, continuously generating ground magnetic Pc5 ULF oscillations during their propagation. This research sheds light on the mechanisms underlying Pc5 ULF wave generation and underscores the role of HFAs in driving magnetospheric‐ionospheric interactions.