MMS observations of kinetic-scale structure in a magnetic depression
Thursday, 17 December 2015: 11:32
2018 (Moscone West)
The Fast Plasma Investigation (FPI) on NASA’s Magnetospheric Multiscale (MMS) spacecraft enables measurement of full three-dimensional velocity distributions of both ions and electrons with an order of magnitude increased temporal resolution over previous magnetospheric instruments. Such high resolution is suitable for resolving dynamics that occur at ion and electron scales throughout Earth’s magnetosphere, in particular in the plasma sheet where low magnetic field magnitudes result in larger particle gyroradii and gyroperiods. Here we present initial data from FPI’s Dual Electron and Dual Ion Spectrometers taken in Earth’s nightside plasma sheet during MMS commissioning. Near the central current sheet, we observe a sub-proton-scale magnetic depression (i.e., 'magnetic hole') containing distinct signatures in the electron data that appear non-gyrotropic in the spacecraft frame of reference. These structures may provide key insights into the small-scale dissipation of energy injected into the magnetosphere via magnetic reconnection in the tail. We will present a detailed examination of the velocity distribution functions of both ions and electrons during this time period and compare with expectations from current theoretical models of magnetic depressions. Although plasma data was only available on a single MMS spacecraft during these events, we are able to leverage Fields data on all four MMS observatories to provide valuable context for the spatial and temporal variation of this magnetic structure.