The Postsunset Vertical Plasma Drift and Its Effects on the Generation of Equatorial Plasma Bubbles Observed by the C/NOFS Satellite

Abstract:

The prereversal enhancement of the vertical plasma drift in the postsunset sector is an important factor that controls the generation of equatorial plasma bubbles. In this study, we use the measurements of the ion velocity meter (IVM) on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite to identify the postsunset ion vertical drift and its effects on the occurrence of plasma bubbles. We only include the events when C/NOFS is located within ±5^o from the magnetic equator during the interval of 1800-1900 LT and lower than 500 km in altitude. In total, we identified 886 events in which plasma bubbles were detected by C/NOFS between 1900 and 2100 LT and 1170 events in which no plasma bubbles were detected during May 2008-June 2013. The ion vertical drift is almost always upward for the 886 cases of occurrence of plasma bubbles, with a mean value of ~40 m/s. The mean ion vertical drift for bubble occurrence increases with the solar radio flux and varies with longitude. The mean ion vertical drift for the cases without plasma bubbles is smaller than 20 m/s, with minimum values near 60^o and 300^o longitude, respectively. There is some overlap in the ion vertical drift between the two categories, with plasma bubbles and without plasma bubbles. The occurrence probability of plasma bubbles increases with the ion upward drift when the ion drift is within 0 and 40 m/s.