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Strong bulk plasma acceleration in Earth's magnetosheath: A magnetic slingshot effect?

Lavraud, B; Borovsky, JE; Ridley, AJ; Pogue, EW; Thomsen, MF; Reme, H; Fazakerley, AN; (2007) Strong bulk plasma acceleration in Earth's magnetosheath: A magnetic slingshot effect? Geophysical Research Letters , 34 (14) , Article L14102. 10.1029/2007GL030024. Green open access

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Abstract

In the near-Earth environment, strong bulk plasma accelerations are frequently taken to be the diagnostic of the occurrence of magnetic reconnection. In this letter, we report new and unambiguous spacecraft observations and corresponding magnetohydrodynamic (MHD) simulation of strong bulk plasma acceleration in the terrestrial magnetosheath during low Alfve n Mach number solar wind conditions, which is demonstrably not associated with magnetic reconnection. We illustrate this effect with Cluster spacecraft data that show plasma accelerations up to speeds of 1040 km/s, while the ambient solar wind speed is only 650 km/ s ( i. e., in excess by 60%). Based on a comparison with global MHD simulations of the magnetosphere, we show that the acceleration results from enhanced magnetic forces exerted on the plasma by '' stiff '' magnetic flux tubes in a low-beta magnetosheath that result from the low Alfven Mach number solar wind. The MHD simulations demonstrate that the acceleration is asymmetric, as well as the magnetopause shape, and is the result of both magnetic pressure gradient and tension forces, showing that this effect is not a simple analogy to a '' slingshot effect '' for which magnetic tension would dominate. Like magnetic reconnection, this mechanism is capable of producing strong plasma acceleration in the near- Earth's environment. The low Alfven Mach number solar wind condition leading to this mechanism is often characteristic of coronal mass ejections (CMEs).

Type: Article
Title: Strong bulk plasma acceleration in Earth's magnetosheath: A magnetic slingshot effect?
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2007GL030024
Publisher version: http://dx.doi.org/10.1029/2007GL030024
Language: English
Additional information: Copyright 2007 by the American Geophysical Union
Keywords: Solar-wind, Dayside magnetopause, Flow, Magnetosphere, Field, Electron, Reconnection, Convection, Boundary, Events
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/165799
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