The Density of Reconnecting Structures Downstream of Earth’s Bow Shock

Abstract

<p>Actively reconnecting, thin current sheets have been observed both within the transition region of Earth&#8217;s bow shock and far downstream into the magnetosheath. Irrespective of whether these structures arise due to shock processes or turbulent dissipation, they are expected to contribute to particle heating and acceleration within their respective regions. In order to assess the integrated impact of the population of thin current sheets on observations of heating and acceleration, we examine shock crossings and extended magnetosheath intervals recorded by the Magnetospheric Multiscale mission (MMS). For each interval we quantify the number density of reconnecting current sheets in the magnetosheath. We estimate the volume associated with each time interval by considering the three-dimensional cone over which Alfv&#233;n and magnetoacoustic waves can propagate within the time interval. We then estimate the number of reconnecting sheets within that volume by comparing heating measures observed within individual sheet crossings with the observed change in those properties across the full interval. Given several extended magnetosheath intervals observed by MMS, we perform our analysis for different locations in the magnetosheath and for different solar wind conditions. In this way we determine the dependence of the number density of thin current sheets on shock orientation (i.e. quasi-parallel or quasi-perpendicular), solar wind transients, and incident plasma parameters.</p>