Pancake pitch angle distributions in warm ions observed with ISEE 1

Abstract

Observations of pancake (peak flux near 90° pitch angle) distributions of low‐energy (≲100 eV) ions are reported. Pancake distributions occur often in H + and He + simultaneously while O + fluxes are either undetectable or field‐aligned. These H + and He + pancake distributions typically display characteristic energies of the order of 10 eV and are frequently mixed with higher density, colder (κT≲3 eV), isotropic, quasi‐Maxwellian components. They appear often within the outer regions of the plasmasphere, and seem to occur most frequently on the dayside and near the magnetic equator.