Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data

Abstract

Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth’s plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong lowâ frequency waves that can heat and accelerate energetic electrons up to the highâ latitude plasma sheet. However, the dynamics of DF propagation and associated lowâ frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a stringâ ofâ pearls configuration with an average intersatellite distance of 160â km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (â ¼500â km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.Key PointsSpatial dynamics of dipolarization fronts are below the ion gyroradiusAssociated whistler wave dynamics have a temporal scale of the order of the ion gyroperiodThe nature of DFs and its implication on associated lowâ frequency waves is discussed