Energetic Particle Sounding of the Magnetopause Deformed by a Hot Flow Anomaly: MMS Observations

Hot flow anomalies (HFAs), which are frequently observed near the Earth’s bow shock, are phenomena resulting from the interaction between interplanetary discontinuities and the Earth’s bow shock. Such transient phenomena upstream of the bow shock can cause significant deformation of the bow shock and the magnetopause, generating traveling convection vortices, field-aligned currents, and ULF waves in the Earth’s magnetosphere. A large HFA lasting about 16 minutes was observed by MMS on November 19, 2015. In this study, energetic particle sounding method with high time resolution (150 ms) Fast Plasma Investigation (FPI) data is used to determine the deformed magnetopause distances, orientations, and structures during the interval when MMS crossed the deformed magnetopause. The estimated radius of curvature of the deformed magnetopause is 2.2 R_E.