Controlling effect of the pitch angle scattering rates near the edge of the loss cone on electron lifetimes

Intense interest currently exists in quantification of the loss of relativistic electrons in the outer radiation belts. Using diffusion coefficients computed for parallel propagating chorus waves, the evolution of the electron pitch angle distribution is examined. Sensitivity numerical experiments show that electron lifetimes are most sensitive to the value of the pitch angle scattering rate near the edge of the loss cone. When the scattering rates do not drop by more than an order of magnitude of the value near the edge of the loss cone for a 30 degree range of pitch angles, we find that the pitch angle distribution reaches an equilibrium shape within hours of the simulations and then decays exponentially with the same rate at all equatorial pitch angles. Implications of the results for combined scattering by EMIC and chorus or hiss waves are discussed as well as implications for future modeling and comparison with observations.