Externally Driven Onset of Localized Magnetic Reconnection and Disruption in a Magnetotail Configuration

Abstract

The response of a magnetotail equilibrium containing dipole magnetic field and plasma sheet regions to the imposition of a longitudinally limited, high‐latitude driving electric field is investigated using 3‐D particle‐in‐cell simulations. The initial response involves a reduction in the equatorial Bz field that is then followed by the development of a dawn‐dusk asymmetric thin current sheet relative to the meridian plane of the driving field. Continued driving leads to the onset of localized reconnection and the emergence of magnetic flux ropes. The cross‐tail extent of the reconnection expands but remains limited to ∼30di, where di is the ion inertia length. A later stage involves disruption of the plasma sheet earthward of the initial X‐line with the formation of multiple field‐aligned currents connecting to the earthward boundary and strong local energization of the ions (4 times thermal) and electrons (10 times thermal). These results demonstrate the ability of a high‐latitude disturbance that may be connected to dayside flow channels to initiate localized magnetic reconnection and disruption in the magnetotail.

Formation of Dawn‐Dusk Asymmetry in Earth's Magnetotail Thin Current Sheet: A Three‐Dimensional Particle‐In‐Cell Simulation

“…Although reconnection had a higher chance to start on the duskside, the specific onset location depended on the shape of B z fluctuations that drove the field toward zero. In this simulation run, the fluctuation that first broke through zero did not occur on the duskside but occurred at y ≈ 0 (Pritchett & Lu, ). Whether this is a statistical coincidence needs further study.…”

“…The thinning of the current sheet and reduction of B z field in response to the driving field eventually would lead to magnetic reconnection and explosive disruption as presented in detail in the companion paper (Pritchett & Lu, ). In the present paper we focused on the TCS asymmetry, and this asymmetry enabled the onset of reconnection preferentially on the duskside, because the strongest reduction of B z occurred there, over a region ~5 d i wide.…”

“…The driving field compresses the magnetotail plasma sheet to form a TCS at its center, and the asymmetry grows self-consistently thereafter. This simulation resolves the entire externally driven evolution in the magnetotail configuration including three stages: (1) dawn-dusk asymmetry formation in the TCS, (2) onset of localized reconnection, and (3) explosive disruption of the current sheet, as presented in the companion paper (Pritchett & Lu, 2018). This paper focuses on the first stage, that is, formation of the asymmetry, and it is organized as follows: the PIC model is described in section 2.…”

Global View of Current Sheet Thinning: Plasma Pressure Gradients and Large‐Scale Currents

“…We have demonstrated that CS thinning is accompanied by formation of ∂p 0 / ∂y gradients directed from the flanks toward midnight. This process makes a thin CS a 3‐D structure, as it was considered in several theoretical models (Birn et al, ; Hsieh & Otto, ; Pritchett & Lu, ). Let us now discuss processes closely related to the formation of ∂p 0 / ∂y gradients: (1) plasma characteristic evolution, (2) plasma convection during CS thinning, and (3) plasma convection after dipolarization.…”

“…As envisioned theoretically and supported by simulations, a generalized 3‐D scenario of CS thinning relies on dawn‐dusk ( ∂ / ∂y ) gradients and plasma flows (e.g., Birn et al, ; Hsieh & Otto, ; Pritchett & Lu, ; Yang et al, ). Combining an external driver with internal magnetotail properties localizes the thin CS around midnight but biased toward the dusk flank (e.g., Lu et al, , ).…”