Parameterization of radiation belt electron loss timescales due to interactions with chorus waves

Wave-particle interactions lead to the loss of relativistic electrons from the outer radiation belt on timescales ranging from hours to weeks. For a fixed value of chorus wave amplitudes pitch-angle diffusion coefficients are computed for a range of energies and L, and are related to the loss rates of radiation belt electrons. By analyzing the dependence of the loss rates on L-value and energy we find functional dependencies for the lifetime of the radiation belt electrons. Parameters of the functional dependences are obtained using a linear regression technique. To create parameterizations of loss rate as a function of geomagnetic indices, we also analyzed the statistical data from day-side lower band chorus observations in the range of geomagnetic latitudes from 20° to 30°. The combined parameterizations of the wave amplitudes and scattering rates indicate that electron loss due to chorus waves strongly depends on energy and geomagnetic activity. During storm-time conditions the lifetimes of relativistic electrons, in the heart of the outer zone are on the order of a day and are on the scale of hours at lower energies. Pitch-angle scattering by chorus waves thus plays an important role in radiation belt dynamics. The developed parameterizations may be used in particle tracing codes and radial diffusion codes. The limitations of the parameterization, effect of scattering by other waves, and local acceleration processes are also discussed.

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