Abstract
Abstract. Fast plasma flows produced as outflow jets from reconnection sites or X lines are a key feature of the dynamics in the Earth's magnetosphere. We have used a polar plane simulation of the hybrid-Vlasov model Vlasiator, driven by steady southward interplanetary magnetic field and fast solar wind, to study fast plasma sheet ion flows and related magnetic field structures in the Earth's magnetotail. In the simulation, lobe reconnection starts to produce fast flows after the increasing pressure in the lobes has caused the plasma sheet to thin sufficiently. The characteristics of the earthward and tailward fast flows and embedded magnetic field structures produced by multi-point tail reconnection are in general agreement with spacecraft measurements reported in the literature. The structuring of the flows is caused by internal processes: interactions between major X points determine the earthward or tailward direction of the flow, while interactions between minor X points, associated with leading edges of magnetic islands carried by the flow, induce local minima and maxima in the flow speed. Earthward moving flows are stopped and diverted duskward in an oscillatory (bouncing) manner at the transition region between tail-like and dipolar magnetic fields. Increasing and decreasing dynamic pressure of the flows causes the transition region to shift earthward and tailward, respectively. The leading edge of the train of earthward flow bursts is associated with an earthward propagating dipolarization front, while the leading edge of the train of tailward flow bursts is associated with a tailward propagating plasmoid. The impact of the dipolarization front with the dipole field causes magnetic field variations in the Pi2 range. Major X points can move either earthward or tailward, although tailward motion is more common. They are generally not advected by the ambient flow. Instead, their velocity is better described by local parameters, such that an X point moves in the direction of increasing reconnection electric field strength. Our results indicate that ion kinetics might be sufficient to describe the behavior of plasma sheet bulk ion flows produced by tail reconnection in global near-Earth simulations. Keywords. Magnetospheric physics (magnetospheric configuration and dynamics; plasma sheet) – space plasma physics (numerical simulation studies)
Highlights
Earthward transport of energy, mass, and magnetic flux on the nightside of the Earth’s magnetosphere occurs mainly through high-speed plasma flows, often in association with substorm activity (Baumjohann et al, 1989; Angelopoulos et al, 1994; Juusola et al, 2011b)
We have examined the substructure of bursty bulk flows (BBFs)-type flow events produced by multiple X point near-Earth tail reconnection in Vlasiator
The flow event in the fast solar wind and southward interplanetary magnetic field (IMF) Vlasiator run agrees in many aspects with the observations recorded in the literature: tail reconnection starts to produce fast flows after the increasing pressure in the lobes www.ann-geophys.net/36/1183/2018/
Summary
Mass, and magnetic flux on the nightside of the Earth’s magnetosphere occurs mainly through high-speed plasma flows, often in association with substorm activity (Baumjohann et al, 1989; Angelopoulos et al, 1994; Juusola et al, 2011b). Earthward flows are typically observed as localized (a few Earth radii wide channels), short-lived ( ∼ 10 min) events during which brief (∼ 1 min) high-speed (> 400 km s−1) flow bursts alternate with near-stagnant plasma (Baumjohann et al, 1989; Baumjohann et al, 1990). Such events are termed bursty bulk flows (BBFs; Angelopoulos et al, 1992). The processes leading to the structuring of the flows and their interaction with the ambient magnetosphere are not yet fully understood.
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