Magnetic local time asymmetries in precipitating electron and proton populations with and without substorm activity

Abstract

The magnetic local time (MLT) dependence of electron (0.15-300 keV) and proton (0.15-6900 keV) precipitation into the atmosphere based on National Oceanic and Atmospheric Administration POES and METOP satellite data during 2001-2008 was described. Using modified APEX coordinates the influence of particle energy, substorm activity and geomagnetic disturbance on the MLT flux distribution was statistically analysed. Some of the findings are the following. a. Substorms mostly increase particle precipitation in the night sector by about factor 2-4, but can also reduce it in the day sector. b. MLT dependence can be assigned to particles entering the magnetosphere at the cusp region and magnetospheric particles in combination with energy-specific drifts (in agreement with Newell et al., 2009). c. MLT flux differences of up to 2 orders of magnitude have been identified inside the auroral oval during geomagnetically disturbed conditions. The novelty here is the comprehensive coverage of energy bands and the focus on asymmetry. d. The maximum flux asymmetry ratio depends on particle energy, decreasing with Kp for low energetic particles and increasing with Kp for higher energy electrons, while high energy protons show a more complex dependency. While some aspects may already have been known, the quantification of the flux asymmetry sheds new light on MLT variation.