The importance of atmospheric precipitation in storm-time relativistic electron flux drop outs

During the sudden decrease of geosynchronous electron flux (> 2 MeV) of 17: 10 - 17: 20 UT, January 21, 2005 large-scale precipitation into the atmosphere was observed. Estimates from ground-based radio propagation experiments at L similar to 5 in the Northern and Southern hemispheres suggest that the atmospheric precipitation was less than 1/10 of the flux apparently lost during this 10 minute period. However, continuing precipitation losses from 4 < L < 6, observed for the next 2.7 hours, provides about 1/2 of the total relativistic electron content lost.