Analysis of the low-altitude proton flux asymmetry: methodology

Existing East-West asymmetry models of the trapped proton fluxes at low alt itudes depend on the local magnetic dip angle and a density scale height de rived from atmospheric models. We propose an alternative approach which map s the directional flux over a drift shell (B-m, L) in terms of the local pi tch and azimuthal angles alpha and beta, where beta is defined in the local mirror plane as the angle between the proton arrival direction and the sur face normal to the drift shell. This approach has the advantage that it onl y depends on drift shell parameters and does not involve an atmosphere mode l. A semi-empirical model based on the new methodology is able to reproduce the angular distribution of a set of SAMPEX/PET proton flux measurements. Guidelines are proposed for spacecraft missions and data analysis procedure s that are intended to be used for the building of new trapped radiation en vironment models. (C) 1999 Elsevier Science Ltd. All rights reserved.