Incorporating spectral characteristics of Pc5 waves into three-dimensional radiation belt modeling and the diffusion of relativistic electrons
The influence of ultralow frequency (ULF) waves in the Pc5 frequency range on radiation belt electrons in a compressed dipole magnetic field is examined. This is the first analysis in three dimensions utilizing model ULF wave electric and magnetic fields on the guiding center trajectories of relativistic electrons. A model is developed, describing magnetic and electric fields associated with poloidal mode Pc5 ULF waves. The frequency and L dependence of the ULF wave power are included in this model by incorporating published ground-based magnetometer data. It is demonstrated here that realistic spectral characteristics play a significant role in the rate of diffusion of relativistic electrons via drift resonance with poloidal mode ULF waves. Radial diffusion rates including bounce motion show a weak pitch angle dependence for αeq >= 50\textdegree (λ <= 20\textdegree) for a power spectral density which is L-independent. The data-based model for greater power at higher L values yields stronger diffusion at αeq = 90\textdegree. The L6 dependence of the diffusion coefficient which is obtained for a power spectral density which is L-independent is amplified by power spectral density which increases with L. During geomagnetic storms when ULF wave power is increased, ULF waves are a significant driver of increased fluxes of relativistic electrons inside geosynchronous orbit. Diffusion timescales obtained here, when frequency and L dependence comparable to observations of ULF wave power are included, support this conclusion.
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Journal of Geophysical Research