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Variations of high-latitude geomagnetic pulsation frequencies: a comparison of time-of-flight estimates and IMAGE magnetometer observations

Variations of high-latitude geomagnetic pulsation frequencies: a comparison of time-of-flight estimates and IMAGE magnetometer observations
Variations of high-latitude geomagnetic pulsation frequencies: a comparison of time-of-flight estimates and IMAGE magnetometer observations

The fundamental eigenfrequencies of standing Alfvén waves on closed geomagnetic field lines are estimated for the region spanning 5.9≤L < 9.5 over all MLT (Magnetic Local Time). The T96 magnetic field model and a realistic empirical plasma mass density model are employed using the time-of-flight approximation, refining previous calculations that assumed a relatively simplistic mass density model. An assessment of the implications of using different mass density models in the time-of-flight calculations is presented. The calculated frequencies exhibit dependences on field line footprint magnetic latitude and MLT, which are attributed to both magnetic field configuration and spatial variations in mass density. In order to assess the validity of the time-of-flight calculated frequencies, the estimates are compared to observations of FLR (Field Line Resonance) frequencies. Using IMAGE (International Monitor for Auroral Geomagnetic Effects) ground magnetometer observations obtained between 2001 and 2012, an automated FLR identification method is developed, based on the cross-phase technique. The average FLR frequency is determined, including variations with footprint latitude and MLT, and compared to the time-of-flight analysis. The results show agreement in the latitudinal and local time dependences. Furthermore, with the use of the realistic mass density model in the time-of-flight calculations, closer agreement with the observed FLR frequencies is obtained. The study is limited by the latitudinal coverage of the IMAGE magnetometer array, and future work will aim to extend the ground magnetometer data used to include additional magnetometer arrays.

Field line eigenfrequencies, Field line resonances, IMAGE, Mass density, Time-of-flight, ULF waves
2169-9380
Sandhu, J.K.
f7695906-560e-4688-ab02-c387ebc5afc7
Yeoman, T.K.
cc3f7732-a6a5-462e-aa81-289804631314
James, M.K.
73103e64-a9cf-4d36-870d-7e2aee93d06d
Rae, I.J.
25677763-0501-4b69-859e-fab930260c69
Fear, R.C.
8755b9ed-c7dc-4cbb-ac9b-56235a0431ab
Sandhu, J.K.
f7695906-560e-4688-ab02-c387ebc5afc7
Yeoman, T.K.
cc3f7732-a6a5-462e-aa81-289804631314
James, M.K.
73103e64-a9cf-4d36-870d-7e2aee93d06d
Rae, I.J.
25677763-0501-4b69-859e-fab930260c69
Fear, R.C.
8755b9ed-c7dc-4cbb-ac9b-56235a0431ab

Sandhu, J.K., Yeoman, T.K., James, M.K., Rae, I.J. and Fear, R.C. (2018) Variations of high-latitude geomagnetic pulsation frequencies: a comparison of time-of-flight estimates and IMAGE magnetometer observations. Journal of Geophysical Research: Space Physics. (doi:10.1002/2017JA024434).

Record type: Article

Abstract

The fundamental eigenfrequencies of standing Alfvén waves on closed geomagnetic field lines are estimated for the region spanning 5.9≤L < 9.5 over all MLT (Magnetic Local Time). The T96 magnetic field model and a realistic empirical plasma mass density model are employed using the time-of-flight approximation, refining previous calculations that assumed a relatively simplistic mass density model. An assessment of the implications of using different mass density models in the time-of-flight calculations is presented. The calculated frequencies exhibit dependences on field line footprint magnetic latitude and MLT, which are attributed to both magnetic field configuration and spatial variations in mass density. In order to assess the validity of the time-of-flight calculated frequencies, the estimates are compared to observations of FLR (Field Line Resonance) frequencies. Using IMAGE (International Monitor for Auroral Geomagnetic Effects) ground magnetometer observations obtained between 2001 and 2012, an automated FLR identification method is developed, based on the cross-phase technique. The average FLR frequency is determined, including variations with footprint latitude and MLT, and compared to the time-of-flight analysis. The results show agreement in the latitudinal and local time dependences. Furthermore, with the use of the realistic mass density model in the time-of-flight calculations, closer agreement with the observed FLR frequencies is obtained. The study is limited by the latitudinal coverage of the IMAGE magnetometer array, and future work will aim to extend the ground magnetometer data used to include additional magnetometer arrays.

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Sandhu_et_al-2018-Journal_of_Geophysical_Research__Space_Physics - Version of Record
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Accepted/In Press date: 11 January 2018
e-pub ahead of print date: 16 January 2018
Published date: 29 January 2018
Keywords: Field line eigenfrequencies, Field line resonances, IMAGE, Mass density, Time-of-flight, ULF waves

Identifiers

Local EPrints ID: 417885
URI: https://eprints.soton.ac.uk/id/eprint/417885
ISSN: 2169-9380
PURE UUID: 5f6a2ef9-99c1-41ee-bad0-22c1cff30b70
ORCID for R.C. Fear: ORCID iD orcid.org/0000-0003-0589-7147

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Date deposited: 16 Feb 2018 17:30
Last modified: 03 Dec 2019 01:35

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Contributors

Author: J.K. Sandhu
Author: T.K. Yeoman
Author: M.K. James
Author: I.J. Rae
Author: R.C. Fear ORCID iD

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