Relativistic electron enhancements, magnetic storms, and substorm activity

The relativistic electron fluxes of the Earth's outer radiation belt are subjected to strong temporal variations. The most prominent changes are initiated by fast solar wind streams impinging upon the magnetosphere, which often also cause enhanced substorm activity and magnetic storms. Using 4 years of data from the particle detector REM aboard the UK satellite Strv-1b in a GTO, we investigated the relation between these different appearances of geomagnetic activity. A typical sequence is that there is a drop in the relativistic electron intensity during the main phase of the magnetic storm and a successive enhancement during the recovery phase which sometimes leads to much higher than pre-storm fluxes. Whereas the flux drop is well correlated with the magnetic storm intensity and is mainly due to the deceleration and loss of particles caused by the ring-current-induced magnetic field changes, there is only a bad correlation between the post-storm electron flux and Dst. As we show here, it is much more the level of substorm activity during the whole event which determines the size of the flux enhancements. (C) 2002 Elsevier Science Ltd. All rights reserved.