Testing global storm‐time electric field models using particle spectra on multiple spacecraft

Abstract

During a magnetic storm on 17–18 February 1998, several spacecraft sampled the inner magnetosphere over a wide range of L shells simultaneously and provided a unique opportunity to obtain particle spectra as a function of L shells, latitude, and local time. We present phase space modeling in a dipole magnetic field and with model electric fields during the recovery phase of that storm to explain the ion spectrograms obtained on three spacecraft (POLAR, EQUATOR‐S, and FAST). The particle signatures studied are from the late recovery phase of the storm, but the particles are affected by the electric fields along their trajectories also during main phase. Our goal is to test and possibly improve global electric field models, which are crucial to the evolution of the storm‐time particle distributions. We backtrace ion distributions from the satellite locations and keep track of charge exchange losses. We use the Volland‐Stern, Weimer 96, Weimer 2000, and modifications of Weimer models to best fit instantaneous potential measurements made by the electric field instrument on POLAR and the ion drift meter instrument on the Defense Meteorological Satellite Program fleet of satellites. We incorporate corotation and a simple, global axisymmetric inductive electric field due to the ring current changes. Significant differences with ion spectral observations do exist and cannot be accounted for simply by modification of existing models. Explaining those differences requires addition of local inductive electric fields or nightside injections.