摘要：We consider two types of events, identified by decreases in Dst below a threshold value and increases in the equatorial mass density at geosynchronous altitudes, ρeq, above a threshold value using the Takahashi et al. (2010) data set. From the Dst events and 1 day averages, we find that there is a statistically weak and small-amplitude difference between ρeq on the day of the event and the days before and after. When hourly averages are considered, a significant peak is found to occur 6 h after event onset, and the primary factor that determines the postonset peak amplitude in ρeq is elevated F10.7. In addition, for hourly averages, ρeq following the onset of a Dst event depends on the north-south component of the interplanetary magnetic field, Bz, after the time of onset, with higher average Bz 4 h after the event onset corresponding to larger ρeq values 7–11 h after onset. From the ρeq events, we find a weak dependence on Bz after the onset of an event, with higher average Bz 4 h after the event onset corresponding to larger ρeq values 24–36 h after onset.
