wharton-ulf-storm-2019JA027648.pdf (12.59 MB)
Download file

The Changing Eigenfrequency Continuum During Geomagnetic Storms: Implications for Plasma Mass Dynamics and ULF Wave Coupling

Download (12.59 MB)
journal contribution
posted on 17.03.2021, 10:31 by SJ Wharton, IJ Rae, JK Sandhu, M-T Walach, DM Wright, TK Yeoman
Geomagnetic storms are one of the most energetic space weather phenomena. Previous studies have shown that the eigenfrequencies of ultralow frequency (ULF) waves on closed magnetic field lines in the inner magnetosphere decrease during storm times. This change suggests either a reduction in the magnetic field strength and/or an increase in its plasma mass density distribution. We investigate the changes in local eigenfrequencies by applying a superposed multiple-epoch analysis to cross-phase spectra from 132 geomagnetic storms. Six ground magnetometer pairs are used to investigate variations from approximately 3 < L < 7 and across the whole dayside sector. We find that at L > 4, the eigenfrequencies decrease by as much as 50% relative to their quiet time values. Both a decrease in magnetic field strength and an increase in plasma mass density, in some locations by more than a factor of 2, are responsible for this reduction. The enhancement of the ring current and an increase in oxygen ion density could explain these observations. At L < 4, the eigenfrequencies increase due to the decrease in plasma mass density caused by plasmaspheric erosion.

Funding

Natural Environment Research Council (NERC). Grant Numbers: NE/L002493/1, NE/P017185/1, NE/P001556/1, NE/P017150/1, NE/P017185/1

RCUK | Science and Technology Facilities Council (STFC). Grant Numbers: ST/S000240/1, ST/N000722/1, ST/S000429/1

History

Citation

Volume 125, Issue 6, June 2020, e2019JA027648

Published in

Journal of Geophysical Research: Space Physics

Volume

125

Issue

6

Publisher

Wiley for American Geophysical Union (AGU)

eissn

2169-9402

Acceptance date

12/05/2020

Copyright date

2020

Available date

17/03/2021

Language

English