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MESSENGER observations of flux ropes in Mercury's magnetotail

MESSENGER observations of flux ropes in Mercury's magnetotail
MESSENGER observations of flux ropes in Mercury's magnetotail

Abstract We report an investigation of magnetic reconnection in Mercury's magnetotail conducted with MESSENGER Magnetometer and Fast Imaging Plasma Spectrometer measurements during seven "hot seasons" when the periapsis of the spacecraft orbit is on Mercury's dayside. Flux ropes are formed in the cross-tail current sheet by reconnection. We have analyzed 49 flux ropes observed between 1.7 RM and 2.8 RM (where RM is Mercury's radius, or 2440 km) down the tail from the center of the planet, for which minimum variance analysis indicates that the spacecraft passed near the central axis of the structure. An average Alfvén speed of 465 km s-1 is measured in the plasma sheet surrounding these flux ropes. Under the assumption that the flux ropes moved at the local Alfvén speed, the mean duration of 0.74±0.15 s determined for these structures implies a typical diameter of ∼345 km, or ∼0.14 RM, which is comparable to a proton gyroradius in the plasma sheet of ∼380 km. We successfully fit the magnetic signatures of 16 flux ropes to a force-free model. The mean radius and core field determined in this manner were ∼450 km, or ∼0.18 RM, and ∼40 nT, respectively. A superposed epoch analysis of the magnetic field during these events shows variations similar to those observed at Earth, including the presence of a post-plasmoid plasma sheet, filled with disconnected magnetic flux, but the timescales are 40 times shorter at Mercury. The results of this flux rope survey indicate that intense magnetic reconnection occurs frequently in the cross-tail current layer of this small but extremely dynamic magnetosphere.

Magnetic flux ropes, Magnetic reconnection, Magnetospheric physics, Mercury's magnetotail
0032-0633
77-89
DiBraccio, Gina A.
03bc93ab-9f5f-46fa-ab81-d986bafba413
Slavin, James A.
18c6ffa4-123f-47db-a157-2d8865090bbd
Imber, Suzanne M.
d84e4b3a-07d1-4ceb-b7e4-730cad46e7e0
Gershman, Daniel J.
00afda5d-e397-4629-b978-12058b1f7c72
Raines, Jim M.
161103e8-53ae-4fa8-a739-1c1e089a3c3f
Jackman, Caitriona M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Boardsen, Scott A.
feec17f2-f168-4f85-a04b-86acdd90fb9d
Anderson, Brian J.
c30e4de5-7757-4c54-a05d-43369e879c0c
Korth, Haje
47ef62e1-890c-46c6-8d1f-b715ba2b1cca
Zurbuchen, Thomas H.
ac644e64-fc28-45cf-af07-14fd57163941
McNutt, Ralph L.
befc4bd1-947b-4111-ae8f-c6489e52634a
Solomon, Sean C.
539a6032-572d-4d27-bbeb-da7ba6d925a1
DiBraccio, Gina A.
03bc93ab-9f5f-46fa-ab81-d986bafba413
Slavin, James A.
18c6ffa4-123f-47db-a157-2d8865090bbd
Imber, Suzanne M.
d84e4b3a-07d1-4ceb-b7e4-730cad46e7e0
Gershman, Daniel J.
00afda5d-e397-4629-b978-12058b1f7c72
Raines, Jim M.
161103e8-53ae-4fa8-a739-1c1e089a3c3f
Jackman, Caitriona M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Boardsen, Scott A.
feec17f2-f168-4f85-a04b-86acdd90fb9d
Anderson, Brian J.
c30e4de5-7757-4c54-a05d-43369e879c0c
Korth, Haje
47ef62e1-890c-46c6-8d1f-b715ba2b1cca
Zurbuchen, Thomas H.
ac644e64-fc28-45cf-af07-14fd57163941
McNutt, Ralph L.
befc4bd1-947b-4111-ae8f-c6489e52634a
Solomon, Sean C.
539a6032-572d-4d27-bbeb-da7ba6d925a1

DiBraccio, Gina A., Slavin, James A., Imber, Suzanne M., Gershman, Daniel J., Raines, Jim M., Jackman, Caitriona M., Boardsen, Scott A., Anderson, Brian J., Korth, Haje, Zurbuchen, Thomas H., McNutt, Ralph L. and Solomon, Sean C. (2015) MESSENGER observations of flux ropes in Mercury's magnetotail. Planetary and Space Science, 115, 77-89, [3883]. (doi:10.1016/j.pss.2014.12.016).

Record type: Article

Abstract

Abstract We report an investigation of magnetic reconnection in Mercury's magnetotail conducted with MESSENGER Magnetometer and Fast Imaging Plasma Spectrometer measurements during seven "hot seasons" when the periapsis of the spacecraft orbit is on Mercury's dayside. Flux ropes are formed in the cross-tail current sheet by reconnection. We have analyzed 49 flux ropes observed between 1.7 RM and 2.8 RM (where RM is Mercury's radius, or 2440 km) down the tail from the center of the planet, for which minimum variance analysis indicates that the spacecraft passed near the central axis of the structure. An average Alfvén speed of 465 km s-1 is measured in the plasma sheet surrounding these flux ropes. Under the assumption that the flux ropes moved at the local Alfvén speed, the mean duration of 0.74±0.15 s determined for these structures implies a typical diameter of ∼345 km, or ∼0.14 RM, which is comparable to a proton gyroradius in the plasma sheet of ∼380 km. We successfully fit the magnetic signatures of 16 flux ropes to a force-free model. The mean radius and core field determined in this manner were ∼450 km, or ∼0.18 RM, and ∼40 nT, respectively. A superposed epoch analysis of the magnetic field during these events shows variations similar to those observed at Earth, including the presence of a post-plasmoid plasma sheet, filled with disconnected magnetic flux, but the timescales are 40 times shorter at Mercury. The results of this flux rope survey indicate that intense magnetic reconnection occurs frequently in the cross-tail current layer of this small but extremely dynamic magnetosphere.

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More information

e-pub ahead of print date: 18 December 2014
Published date: 1 September 2015
Keywords: Magnetic flux ropes, Magnetic reconnection, Magnetospheric physics, Mercury's magnetotail

Identifiers

Local EPrints ID: 436461
URI: http://eprints.soton.ac.uk/id/eprint/436461
ISSN: 0032-0633
PURE UUID: d784224d-848b-4a4b-a9f2-1743c7846a26
ORCID for Caitriona M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

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Date deposited: 11 Dec 2019 17:30
Last modified: 19 Oct 2020 16:34

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Contributors

Author: Gina A. DiBraccio
Author: James A. Slavin
Author: Suzanne M. Imber
Author: Daniel J. Gershman
Author: Jim M. Raines
Author: Caitriona M. Jackman ORCID iD
Author: Scott A. Boardsen
Author: Brian J. Anderson
Author: Haje Korth
Author: Thomas H. Zurbuchen
Author: Ralph L. McNutt
Author: Sean C. Solomon

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