Stopping flow bursts and their role in the generation of the substorm current wedge

Abstract

Key Points:• Flow burst stops where its entropy is nearly equal to entropy of ambient plasma • Flow burst modifies pressure and entropy distribution in the inner magnetosphere • Long relaxation time after the FB subsided provides long-duration SCW effects Supporting Information:• Readme • Figure S1.pdf • Figure S2.pdf • Figure S3.pdf • Figure S4.pdf fortuitously stopped at ∼ 9 Re within a unique, compact multispacecraft constellation for the duration of a 30 min long substorm current wedge-related dipolarization. Observations inside and outside the halted flow burst indicate that it retained properties (including a narrow DF, a localized compression region ahead of it, and its structured, low density, low entropy (pV 5∕3 ) content) when arrived at its stopping point, where the entropy of the ambient plasma was nearly equal to that of the flow burst. We show that even short-duration flow bursts can significantly modify pressure and entropy distributions in the inner magnetosphere. The new distribution takes a long time to relax (a few tens of minutes, consistent with substorm recovery time scales). We argue that these pressure and entropy changes resulting from the incoming flow bursts can be responsible for the support/generation of a substorm current wedge.

Acceleration of ions by electric field pulses in the inner magnetosphere

“…The increased B z magnetic field component and plasma flows v x , v y ∼ 50–200 km/s indicate that plasma jets accompanied by dipolarization fronts penetrate the inner magnetosphere. Relatively small amplitudes of plasma flow velocities v x , v y indicate that dipolarizing flux bundles are observed not far from the braking region, where the growing pressure of the dipole magnetic field stops them [e.g., Dubyagin et al , ; Sergeev et al , , and references therein]. In all three events, we observe strong electric field pulse (components E y , E x ) with amplitudes ∼–15 mV/m.…”

Jets Downstream of Collisionless Shocks

“…32) and global simulations (e.g., Wiltberger et al 2015). As discussed by Sergeev et al (2014) and illustrated by Fig. 32, every flow burst brings additional magnetic flux and increases the plasma pressure in a local part of the inner region (see also Fig.…”

On application of asymmetric Kan-like exact equilibria to the Earth magnetotail modeling

“…This quantity is chosen due to its importance for the magnetotail dynamics. As was claimed by Birn et al (2009) and verified by in situ data analysis (Sergeev et al, 2014), any bursty bulk flow (BBF), produced by reconnection in the magnetotail and moving toward the Earth, stops near that particular point where the entropy of the ambient plasma is equal to that inside the BBF. The distribution of entropy along the magnetotail is also an important factor for the stability analysis (Birn et al, 2009) and for the study of wave (oscillation) generation and dissipation (Panov et al, 2016).…”

“…In applications to collisionless plasma, the background equilibrium is to be derived from a solution of the kinetic Vlasov-Maxwell equations. A number of such solutions are derived both numerically (e.g., Burkhart et al, 1992;Pritchett and Coroniti, 1992;Cargill et al, 1994, and others) and analytically (e.g., Schindler and Birn, 2002;Yoon and Lui, 2005;Sitnov and Merkin, 2016;Vinogradov et al, 2016). All these solutions describe symmetric planar current sheets; the only approximate equilibrium solution for bent CS was introduced in the paper of Panov et al (2012), where the authors present an analysis of direct THEMIS and GOES observations of plasma sheet evolution near substorm onset.…”