Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm11b1736w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM11B-1736
Physics
Plasma Physics
[2716] Magnetospheric Physics / Energetic Particles: Precipitating, [2753] Magnetospheric Physics / Numerical Modeling, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [7867] Space Plasma Physics / Wave/Particle Interactions
Scientific paper
Riometer measurements across the auroral zone have shown that electron precipitation down to the D-layer may be modulated at ULF frequencies. Observations [Spanswick et al., Ann. Geophys. 2005] demonstrate that magnetic ULF wave perturbations are a necessary pre-requisite for the precipitation fluctuations. It has long been argued that the ULF modulation of electron precipitation occurs through a complicated wave-wave interaction: long-period ULF waves in the magnetosphere modify the growth-rates of whistler-mode waves, which in turn modulate pitch-angle scattering, leading to fluctuations in the precipitation of electrons from regions close to the equatorial plane [Coroniti & Kennel, JGR, 1970; Haugstad, JATP, 1975]. We investigate aspects of this hypothesis by studying the modification of VLF whistler-mode propagation and growth rates by global ULF oscillations in an idealized dipole magnetosphere. A linear ray-tracing algorithm, with growth-rates obtained from the full warm plasma dispersion relation, is used to study millions of growing ray-paths as waves propagate through the magnetosphere in both an unperturbed magnetic field, and one that is perturbed by the presence of a 2mHz global m=0 ULF wave oscillation. The resulting path-integrated wave gains are used to build a picture of the estimated wave growth as a function of frequency, wavevector angle, and propagation angle at different positions in the magnetosphere relative to the equatorial plane. The predicted change in wave spectra by a ULF wave oscillation is used to estimate the change in particle precipitation. These results are compared to estimates from a more direct model of electron precipitation by ULF waves presented by Degeling et al. (this meeting), as well as to measurements of the D-region modulation from the CGSM riometer network.
Degeling A. W.
Donovan Eric F.
Rankin Robert
Spanswick Emma
Watt Colum
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