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Cluster observations of a transient signature in the magnetotail: implications for the mode of reconnection.

Authors :
Beyene, S.
Owen, C. J.
Walsh, A. P.
Forsyth, C.
Fazakerley, A. N.
Kiehas, S.
Dandouras, I.
Lucek, E.
Source :
Annales Geophysicae (ANGEO) (09927689); Nov2011, Vol. 29 Issue 11, p2131-2146, 16p, 3 Diagrams, 9 Graphs
Publication Year :
2011

Abstract

Travelling compression regions (TCRs) are perturbations in the magnetotail lobe magnetic field caused by structures moving Earthward or tailward within the plasma sheet. Previous works have suggested that these structures are created by either time-dependant reconnection occurring at a single X-line, forming a flux-bulge-type structure, or space-variant reconnection at multiple X-lines, forming fluxrope- type structures. In this study we examine an event in which Cluster 2 observed a TCR while the 3 remaining Cluster spacecraft observed the underlying magnetic structure at a range of distances from the neutral sheet. The magnetic structure has a velocity of (99, 154, -31) km s<superscript>-1</superscript> in GSM (∣V∣ = 186 km s<superscript>-1</superscript>), an estimated size of 1.19RE along the direction of travel and a size between 1.94 and 2.86RE in the direction perpendicular to the current sheet. As the structure passes the spacecraft, Cluster 1 and Cluster 4 observed a bipolar signature in BZ, plasma-sheet-like plasma and fieldaligned electron flows. Cluster 3 passed closest to the centre of the structure and observed two separate reductions in the plasma density (with field-aligned electron flows); these drop-outs in the plasma sheet were possibly created by the actions of X-lines. The second drop-out in the plasma sheet also includes a reversal of the ion flow, a signature consistent with the passage of a reconnecting X-line past the spacecraft. Between the X-lines, the plasma outflow from the X-lines caused an increase in pressure which led to a localised expansion of the plasma and also the observations at Cluster 1 and Cluster 4 and the TCR. Our observations do not uniquely match either of the flux rope or the flux bulge predictions although the observation of two plasma sheet drop-outs (interpreted as X-lines, one active, one dormant) with plasmasheet- like between them and only one TCR is a situation expected in multiple X-line reconnection. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
09927689
Volume :
29
Issue :
11
Database :
Complementary Index
Journal :
Annales Geophysicae (ANGEO) (09927689)
Publication Type :
Academic Journal
Accession number :
70105519
Full Text :
https://doi.org/10.5194/angeo-29-2131-2011