Pitch angle distributions of energetic electrons at Saturn

Abstract

Pitch angle distributions of energetic electrons (110-365 keV) at Saturn are statistically analyzed for 2005-2009. Using a nondipolar model magnetic field, pitch angle distributions are mapped to the magnetospheric equator and sorted by equatorial crossing distance. The results are quantified using a standard function for the pitch angle distribution, f(α) = Asin^Kα (where α is the pitch angle and K is the power). Inside of ∼10 R_S, the distributions are mostly peaked at 90° (K < 0), signifying a trapping distribution. Outside of this distance, the distributions are mostly field aligned (K > 0) with maxima near 0° and 180°. The 10 R_S boundary maps to Saturn's ionosphere at latitudes equatorward of the aurora. Very few “flat” distributions are observed (K ≈ 0). The pitch angle distributions are not as well organized in local time as they are in radial distance, but over the 5 year survey between 10 and 20 R_S field-aligned distributions appear most often near midnight, while trapping distributions are found elsewhere.