Physical modelling and experimental investigation of the abrupt afternoon decrease of Cosmic Noise Absorption

Abstract

The amplitude of the substorm-related Cosmic Noise Absorption (CNA) bay often displays significant reduction near the noon MLT meridian in the auroral zone. Statistically the Local Time position of the afternoon CNA depression shows clear dependence on the IMF B Z values during preceding hour. We modelled the drift motion of charged particles (having different energies and pitch angles) in realistic magnetic and electric fields to investigate whether the convection electric field may cause considerable reduction of energetic electron precipitation. We found that the outward convection and deceleration lead to considerable decrease of particle fluxes and changes in their characteristics during particle drift over the noon sector. As a result, we found this effect alone may reduce precipitation by at least 30% over a 3 hour MLT segment of particle drift trajectories close to noon.