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

Low‐energy ions of ionospheric origin with energies below 10s of electron volt dominate most

of the volume and mass of the terrestrial magnetosphere. However, sunlit spacecraft often become

positively charged to several 10s of volts, which prevents low‐energy ions from reaching the particle

detectors on the spacecraft. Magnetospheric Multiscale spacecraft (MMS) observations show that

ultralow‐frequency (ULF) waves drive low‐energy ions to drift in the E × B direction with a drift velocity

equal to VE×B, and low‐energy ions were accelerated to suffificient total energy to be measured by the

MMS/Fast Plasma Investigation Dual Ion Spectrometers. The maximum low‐energy ion energy flflux peak

seen in MMS1's dual ion spectrometer measurements agreed well with the theoretical calculation of H+ ion

E × B drift energy. The density of ions in the energy range below minimum energy threshold was

between 1 and 3 cm−3 in the magnetosphere subsolar region in this event.