Low energy ion pitch angle distributions observed on the dayside at geosynchronous altitudes

Abstract

Pitch angle distributions of low energy (20–400 eV) ions observed at geosynchronous altitudes are found to have field‐aligned components almost 90% of the time on the average from dawn to midafternoon, thereafter decreasing to just less than 50%. Pancake pitch angle component occurrence frequencies vary oppositely, increasing to a peak of 40% in late afternoon. Although the occurrence frequencies for field‐aligned components display no systematic variation with energy, pancake components are observed more often in the lower energy particles. Similarly, magnetic activity is found to have little effect on the occurrence frequencies of field‐aligned components, whereas pancake components occur more frequently under magnetically quiet conditions.