Electron dynamics in a subproton‐gyroscale magnetic hole

Abstract

Magnetic holes are ubiquitous in space plasmas, occurring in the solar wind, downstream of planetary bow shocks, and inside the magnetosphere. Recently, kinetic‐scale magnetic holes have been observed near Earth's central plasma sheet. The Fast Plasma Investigation on NASA's Magnetospheric Multiscale (MMS) mission enables measurement of both ions and electrons with 2 orders of magnitude increased temporal resolution over previous magnetospheric instruments. Here we present data from MMS taken in Earth's nightside plasma sheet and use high‐resolution particle and magnetometer data to characterize the structure of a subproton‐scale magnetic hole. Electrons with gyroradii above the thermal gyroradius but below the current layer thickness carry a current sufficient to account for a ~10–20% depression in magnetic field magnitude. These observations suggest that the size and magnetic depth of kinetic‐scale magnetic holes is strongly dependent on the background plasma conditions.

Kinetics of sub‐ion scale magnetic holes in the near‐Earth plasma sheet

“…Taking MH geometry (as shown by Figure ) into account, we use plasma flows along the x axis to estimate the current density. The electron bulk velocity, v ex , obtained from direct ESA measurements significantly exceeds the ion bulk velocity ( v ex reaches 400 km/s, comparable with previous observations [ Gershman et al , ]). Electrons flow in opposite directions at two hole boundaries, generating current density j ex =− e n e v ex that supports the magnetic field gradients.…”

“…Thus, we can assume that these cold (at energies <1 keV) electrons do not contribute to MH structure. Similar conclusions, but for energies <0.2 keV, were drawn by Gershman et al [].…”

“…Gershman et al [] and Yao et al [] showed that electron distributions within MHs exhibit significant anisotropies with increased transverse fluxes in the 0.2–4 keV energy range. We checked that the electron population below 500 eV does not contribute to the observed electron bulk velocity v ex , and thus only suprathermal particles are responsible for current generation.…”

Observations of a Kinetic‐Scale Magnetic Hole in a Reconnection Diffusion Region

“…Subion scale MHs have been observed both in steady and turbulent plasmas (Gershman et al, 2016;Huang, Du, et al, 2017;Yao et al, 2017;Zhang et al, 2017). Subion scale MHs have been observed both in steady and turbulent plasmas (Gershman et al, 2016;Huang, Du, et al, 2017;Yao et al, 2017;Zhang et al, 2017).…”

“…It has been widely observed in various space plasmas, including the solar wind (Turner et al, 1977;Winterhalter et al, 1995;Zhang et al, 2008), the comet magnetosphere (Russell et al, 1987), the planetary magnetosheath (Balikhin et al, 2009;Cattaneo et al, 1998;Huang, Du, et al, 2017;Joy et al, 2006;Lucek et al, 1999;Tsurutani et al, 1982;Violante et al, 1995), and the magnetosphere (Ge et al, 2011;Gershman et al, 2016;Shi et al, 2009;Sun et al, 2012;Zhang et al, 2017). It has been widely observed in various space plasmas, including the solar wind (Turner et al, 1977;Winterhalter et al, 1995;Zhang et al, 2008), the comet magnetosphere (Russell et al, 1987), the planetary magnetosheath (Balikhin et al, 2009;Cattaneo et al, 1998;Huang, Du, et al, 2017;Joy et al, 2006;Lucek et al, 1999;Tsurutani et al, 1982;Violante et al, 1995), and the magnetosphere (Ge et al, 2011;Gershman et al, 2016;Shi et al, 2009;Sun et al, 2012;Zhang et al, 2017).…”