Solar wind, F10.7, and geomagnetic activity relationship to the equatorial plasma mass density at geosynchronous orbit

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, rho(eq), 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 rho(eq) 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 rho(eq) is elevated F-10.7. In addition, for hourly averages, rho(eq) following the onset of a Dst event depends on the north-south component of the interplanetary magnetic field, B-z, after the time of onset, with higher average B-z 4 h after the event onset corresponding to larger rho(eq) values 7-11 h after onset. From the rho(eq) events, we find a weak dependence on B-z after the onset of an event, with higher average B-z 4 h after the event onset corresponding to larger rho(eq) values 24- 36 h after onset.