Relativistic electron drift shell splitting

A survey of equatorial outer radiation belt relativistic electron pitch angle distributions measured on the Polar satellite shows anisotropies that are consistent with the effects of drift shell splitting. Simulations based on the observed radial intensity gradients and on drift shell calculations in a magnetospheric field model show that for low geomagnetic activity levels, the measured average anisotropies are similar to those predicted. With increasing geomagnetic activity the anisotropies do not change as much as is predicted, particularly on the nightside where the pitch angle distributions have local minima in the direction perpendicular to the magnetic field. At a given location and activity level there is substantial variability in the measured anisotropies about their long‐term averages.