Energetic Outer Zone Electron Loss Timescales During Low Geomagnetic Activity

Following enhanced magnetic activity the fluxes of energetic electrons in the Earths outer radiation belt gradually decay to quiet-time levels. We use CRRES observations to estimate the energetic electron loss timescales and to identify the principal loss mechanisms. Gradual loss of energetic electrons in the region 3.0 or L or 5.0 occurs during quiet periods Kp 3- following enhanced magnetic activity on timescales ranging from 1.5 to 3.5 days for 214kV electrons to 5.5 to 6.5 days for 1.09MeV electrons. The intervals of decay are associated with large average values of the ratio, indicating that the decay takes place in the plasmasphere. We compute loss timescales for pitch-angle scattering by plasmaspheric hiss using the PADIE code with wave properties based on CRRES observations. The resulting timescales suggest that pitch angle scattering by plasmaspheric hiss propagating at small or intermediate wave normal angles is responsible for electron loss over a wide range of energies and L shells.