On the propagation of sudden impulses through the magnetosphere

On the basis of a simple geometrical approach, we evaluated some aspects of the propagation time of SI disturbances between the magnetopause and geostationary orbit for variable impact points at the magnetopause, focusing attention on the expected lag time between the SI manifestation at spacecraft located ≈4 h a part along geostationary orbit. We also examined a set of events identified by GOES8 and GOES10 during 2001-2004. The experimental observations reveal a clear local time (LT) dependence of the lag time between spacecraft that is consistent with that one predicted for disturbances determined by the first launch from the impact point and propagating in different directions approximately with the same speed. In addition, the comparison with the expected LT pattern suggests that most of the events might be related with pressure fronts impacting on the subsolar magnetopause; this aspect is consistent with the dominant orientation of the interplanetary shock fronts for this set of events.