Quantitative Estimations of Relativistic Electron Drift Loss Effect during Geomagnetic Storms

It has been suggested that drift loss to the magnetopause can be one of the major loss mechanisms contributing to relativistic electron flux dropouts. The flux of relativistic electrons that usually decreases during the storm main phase sometimes never recovers to their pre-storm time level at the end of a storm. This suggests the possibility that electrons at high L-shells can move outward aided by the Dst effect and then be drift-lost by encountering the magnetopause, leading to flux dropouts at inner L-shells. In this study, we determine the extent to which the drift loss through the magnetopause as combined with the Dst effect is important to the total loss of the outer radiation belt. We test this effect quantitatively for three groups of magnetic storms as obtained by classifying 95 storms according to their Dst minimum intensities and have performed the calculation of drift paths of relativistic electrons' guiding center under the Tsyganenko T02 model. It is shown that generally a prestorm electron that drifts in an inner region with a particular energy and pitch angle moves outward by the Dst effect and appear at an outer region with a lower energy and pitch angle during the storm main phase. The effect that electrons that do not return back to where it was initially due to the drift loss effect after the full recovery of the storm is seen at regions of r down to 5RE for storms of moderate intensity (-100nTmin<-50nT). For a stronger storm, our calculation indicates that this effect can penetrate into a region even inward of 5RE.