Variations of Field Line Eigenfrequencies With Ring Current Intensity

Sandhu, J. K., Yeoman, T. K. and Rae, Jonathan (2018) Variations of Field Line Eigenfrequencies With Ring Current Intensity. Journal of Geophysical Research: Space Physics, 123 (11). pp. 9325-9339. ISSN 2169-9380

[img]
Preview
Text
2018JA025751.pdf - Published Version
Available under License Creative Commons Attribution 4.0.

Download (2MB) | Preview
Official URL: https://doi.org/10.1029/2018JA025751

Abstract

We present results from the closed magnetosphere (5.9≤L < 9.5 over all magnetic local times) to demonstrate and assess the variations in field line eigenfrequency with geomagnetic activity. Using the time-of-flight technique with realistic magnetic field and mass density models, the spatial distributions of field line eigenfrequencies are determined for a range of different geomagnetic activity levels, as defined by the Dst index. The results indicate that during geomagnetically active conditions, the eigenfrequency of a given field line is generally decreased compared to quiet times, in addition to variations in local asymmetries. By comparing the dependence to changes in the magnetic field and mass density distribution, it is established that the inflation and weakening of the geomagnetic field outweighs decreased plasma mass density and is the sole contributor to decreased eigenfrequencies with increased geomagnetic activity. We highlight the importance of considering the magnetic field, mass density, and average ion mass contributions when using observed eigenfrequencies to probe magnetospheric conditions. Furthermore, the estimates significantly improve upon existing time-of-flight results, through a consideration of mass density changes with geomagnetic activity. We also provide estimates of eigenfrequencies for a comparatively extended spatial region than available from prior direct observations of field line resonances. The results have clear implications for furthering our understanding of how wave energy propagates throughout the magnetosphere during geomagnetic storms.

Item Type: Article
Uncontrolled Keywords: field line resonances, ULF, ring current storms, eigenfrequencies, radiation belts
Subjects: F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 07 Oct 2020 10:49
Last Modified: 07 Oct 2020 11:00
URI: http://nrl.northumbria.ac.uk/id/eprint/44440

Actions (login required)

View Item View Item

Downloads

Downloads per month over past year

View more statistics