MMS multi‐point analysis of FTE evolution: physical characteristics and dynamics

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Title: MMS multi‐point analysis of FTE evolution: physical characteristics and dynamics
Authors: Akhavan‐Tafti, M
Slavin, JA
Eastwood, JP
Cassak, PA
Gershman, DJ
Item Type: Journal Article
Abstract: Previous studies have indicated that flux transfer events (FTEs) grow as they convect away from the reconnection site along the magnetopause. This increase in FTE diameter may occur via adiabatic expansion in response to decreasing external pressure away from the subsolar region or due to a continuous supply of magnetic flux and plasma to the FTEs' outer layers by magnetic reconnection. Here we investigate an ensemble of 55 FTEs at the subsolar magnetopause using Magnetospheric Multiscale (MMS) multi‐point measurements. The FTEs are initially modeled as quasi‐force‐free flux ropes in order to infer their geometry and the spacecraft trajectory relative to their central axis. The MMS observations reveal a radially‐inward net force at the outer layers of FTEs which can accelerate plasmas and fields toward the FTE's core region. Inside the FTEs, near the central axis, plasma density is found to decrease as the axial net force increases. It is interpreted that the axial net force accelerates plasmas along the axis in the region of compressing field lines. Statistical analysis of the MMS observations of the 55 FTEs indicates that plasma pressure, Pth, decreases with increasing FTE diameter, λ, as Pth,obsv ∝ λ−0.24. Assuming that all 55 FTEs started out with similar diameters, this rate of plasma pressure decrease with increasing FTE diameter is at least an order of magnitude slower than the theoretical rate for adiabatic expansion (i.e., Pth,adiab. ∝ λ−3.3), suggesting the presence of efficient plasma heating mechanisms, such as magnetic reconnection, to facilitate FTE growth.
Issue Date: 1-Jul-2019
Date of Acceptance: 7-Jun-2019
ISSN: 2169-9380
Publisher: American Geophysical Union (AGU)
Start Page: 5376
End Page: 5395
Journal / Book Title: Journal of Geophysical Research: Space Physics
Volume: 124
Issue: 7
Copyright Statement: ©2019. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Funder's Grant Number: ST/N000692/1
Publication Status: Published
Article Number: 2018JA026311
Online Publication Date: 2019-06-22
Appears in Collections:Space and Atmospheric Physics
Faculty of Natural Sciences

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