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Comparison between theory and observation of the frequency sweep rates of equatorial rising tone chorus
Author(s) -
Tao X.,
Li W.,
Bortnik J.,
Thorne R. M.,
Angelopoulos V.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl051413
Subject(s) - chorus , earth's magnetic field , physics , sweep frequency response analysis , magnetic field , geophysics , asymmetry , field (mathematics) , frequency scaling , computational physics , geodesy , geology , acoustics , mathematics , art , power (physics) , literature , quantum mechanics , pure mathematics
Theoretical predictions for chorus frequency sweep rates by Helliwell and Trakhtengerts are compared with observations from the THEMIS satellites and a previously published dataset from the Cluster satellites. We first extend the theories to use a general magnetic field model to include the effects of magnetic local time and geomagnetic activity, and then show that both theories give the same dependence of the frequency sweep rate on background plasma parameters. The theoretical scaling of frequency sweep rates are shown to agree very well with observations. We demonstrate that for a given equatorial magnetic field strength, nightside and dawnside chorus waves have higher frequency sweep rates because of the stretching of the magnetic field, while dayside chorus waves have lower frequency sweep rates because of the compression of the field. Increasing geomagnetic activity will enhance the asymmetry by increasing the day‐night asymmetry of the background field. The results are important for understanding the generation mechanism of chorus waves.