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

<p>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<sub>E</sub>.</p>

Magnetospheric Multiscale (MMS) Observations of ULF Waves and Correlated Low-Energy IonMonoenergetic Acceleration

<div>Low‐energy ions of ionospheric origin with energies below 10s of electron volt dominate most</div><div>of the volume and mass of the terrestrial magnetosphere. However, sunlit spacecraft often become</div><div>positively charged to several 10s of volts, which prevents low‐energy ions from reaching the particle</div><div>detectors on the spacecraft. Magnetospheric Multiscale spacecraft (MMS) observations show that</div><div>ultralow‐frequency (ULF) waves drive low‐energy ions to drift in the E × B direction with a drift velocity</div><div>equal to VE×B, and low‐energy ions were accelerated to suffificient total energy to be measured by the</div><div>MMS/Fast Plasma Investigation Dual Ion Spectrometers. The maximum low‐energy ion energy flflux peak</div><div>seen in MMS1's dual ion spectrometer measurements agreed well with the theoretical calculation of H+ ion</div><div>E × B drift energy. The density of ions in the energy range below minimum energy threshold was</div><div>between 1 and 3 cm−3 in the magnetosphere subsolar region in this event.</div>