Abstract
Actively reconnecting, thin current sheets have been observed both within the transition region of Earth'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 prevalence of thin current sheets in the magnetosheath, we examine shock crossings and extended magnetosheath intervals recorded by the magnetospheric multiscale mission (MMS). For each magnetosheath interval, we quantify the prevalence of current sheets in that region of space using: a one-dimensional measure of structures per unit length of observed plasma, a packing factor corresponding to the fraction of time the spacecraft are within current structures, and a three-dimensional measure requiring an estimate of the number of current sheets within an associated volume. We estimate that volume by considering the three-dimensional cone over which Alfvén and magnetoacoustic waves can propagate during each interval. Using 25 extended magnetosheath intervals observed by MMS, we perform our analysis for different locations in the magnetosheath and for different solar wind conditions. We find that the number density of current sheets is higher toward the magnetosheath flanks, that it reduces as a power law with distance from the bow shock, and that it is not strongly influenced by the properties of the upstream bow shock.
Highlights
The magnetosheath region of Earth’s magnetosphere, comprising shocked solar wind plasma bounded by the bow shock and the magnetopause, is observed to be a turbulent medium1–5
The analysis described in this paper has been performed for 25 individual magnetosheath intervals, encompassing all those recorded in high-resolution burst mode for at least 15 minutes each during the period December 2017 to March 2020
The distance to the shock Dsh is taken along the bulk velocity vector, and the shock location is calculated from the Peredo et al33 model scaled to the nearest shock crossing observed by Multiscale mission (MMS)
Summary
The magnetosheath region of Earth’s magnetosphere, comprising shocked solar wind plasma bounded by the bow shock and the magnetopause, is observed to be a turbulent medium. For each magnetosheath interval given, this calculation of the number density of current sheets is repeated for a sliding window of maximum duration ∆t = Dsh /vbulk , where Dsh is the estimated distance to the bow shock from the spacecraft along the vector −vbulk. In this way, we assume that current structures and their indirect effects originate at or downstream of the bow shock.
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