How Solar Wind Controls the Recovery Phase Morphology of Intense Magnetic Storms

Abstract

AbstractGeomagnetic storms are critical space weather phenomena resulting from the interaction between the solar wind and the Earth's magnetosphere. However, most studies focus on the main phase of magnetic storms, leaving the morphology of the recovery phase an open question. In this study, we analyze 82 intense magnetic storms with the minimum Dst index ≤ −100 nT between 1995 and 2018, finding that these storms can be classified into two distinct types: one‐stage recovery storms that exhibit a single rapid exponential recovery and two‐stage recovery storms that are characterized by a rapid exponential recovery in the early recovery phase and a slow linear recovery in the later recovery phase. We find that the two‐stage recovery storms are dominant, accounting for approximately 60% of the events. Interestingly, the proportion of two‐stage recovery storms peaks during solar minimum. The two‐stage recovery storms tend to be accompanied by more Alfvén waves with long‐duration and intense southward interplanetary magnetic fields. In addition, we find that the decay rate of the Dst index in the later recovery phase is correlated with the average BZ of the interplanetary magnetic field when the solar wind has a high degree of Alfvénicity. Overall, our results shed new light on the recovery phase morphology of intense magnetic storms and highlight the role of Alfvén waves in this process.