Solar wind, F 10.7 , and geomagnetic activity relationship to the equatorial plasma mass density at geosynchronous orbit

We consider two types of events, identified by decreases in D s t below a threshold value and increases in the equatorial mass density at geosynchronous altitudes, ρ eq , above a threshold value using the Takahashi et al. (2010) data set. From the D s t events and 1 day averages, we find that there is a statistically weak and small‐amplitude difference between ρ 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 ρ eq is elevated F 10.7 . In addition, for hourly averages, ρ eq following the onset of a D s t 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 ρ eq values 7–11 h after onset. From the ρ 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 ρ eq values 24–36 h after onset.