Observations of discrete magnetosonic waves off the magnetic equator

TitleObservations of discrete magnetosonic waves off the magnetic equator
Publication TypeJournal Article
Year of Publication2015
AuthorsZhima, Z, Chen, L, Fu, H, Cao, J, Horne, R, Reeves, G
JournalGeophysical Research Letters
Date Published12/2015
Keywordsdiscrete structure; magnetsonic wave; off-equatorial region
AbstractFast mode magnetosonic waves are typically confined close to the magnetic equator and exhibit harmonic structures at multiples of the local, equatorial proton cyclotron frequency. We report observations of magnetosonic waves well off the equator at geomagnetic latitudes from −16.5°to −17.9° and L shell ~2.7–4.6. The observed waves exhibit discrete spectral structures with multiple frequency spacings. The predominant frequency spacings are ~6 and 9 Hz, neither of which is equal to the local proton cyclotron frequency. Backward ray tracing simulations show that the feature of multiple frequency spacings is caused by propagation from two spatially narrow equatorial source regions located at L ≈ 4.2 and 3.7. The equatorial proton cyclotron frequencies at those two locations match the two observed frequency spacings. Our analysis provides the first observations of the harmonic nature of magnetosonic waves well away from the equatorial region and suggests that the propagation from multiple equatorial sources contributes to these off-equatorial magnetosonic emissions with varying frequency spacings.
Short TitleGeophys. Res. Lett.

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