References

ANGEO

Annales Geophysicae

ANGEO

Ann. Geophys.

1432-0576

Copernicus Publications

Göttingen, Germany

10.5194/angeo-29-2131-2011

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

Beyene

¹ Owen

C. J.

¹ Walsh

A. P.

¹ Forsyth

¹ Fazakerley

A. N.

¹ Kiehas

² ³ Dandouras

⁴ ⁵ Lucek

⁶

Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, RH5 6NT, UK

Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria

Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA

Institut de Recherche en Astrophysique et Planétologie (IRAP), University of Toulouse, UPS, 9 Ave. du Colonel Roche, B.P. 44346, 31028 Toulouse, France

IRAP, CNRS, B.P. 44346, 31028 Toulouse, France

Space and Atmospheric Physics, Imperial College London, SW7 2BZ, UK

28 11 2011

29 11 2131 2146

2011

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

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The full text article is available as a PDF file from https://angeo.copernicus.org/articles/29/2131/2011/angeo-29-2131-2011.pdf

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 flux-rope-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−1 in GSM (|V| = 186 km s−1), an estimated size of 1.19 RE along the direction of travel and a size between 1.94 and 2.86 RE 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 field-aligned 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 plasma-sheet-like between them and only one TCR is a situation expected in multiple X-line reconnection.

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