Morphology of midlatitude electron density enhancement using total electron content measurements

Using the global ionospheric map of total electron content in 2002-2009, this paper investigates anomalous, midlatitude electron density enhancement (MEDE) bounded by a tropical electron density trough and the usual midlatitude electron density trough at all times (24 h) of the day for the first time. The diurnal, seasonal, and longitudinal variations in the occurrence and strength of MEDE are studied at solar maximum (2002) and long deep solar minimum (2009), and latitude-longitude dependence is examined using the data in 2002-2009. The results show that the MEDE occurs at all times of the day though pronounced at night (2200-0400 LT), and in some cases the daytime occurrence could be more frequent than the corresponding nighttime occurrence. The strength maximizes at around 0400 LT and is weak during daytime. Both the occurrence and strength are, in general, predominant in winter at low solar activity and exhibit significant longitudinal dependence. The E × B drift, strength, and direction of neutral wind and ionosphere-plasmasphere plasma flow and their day-to-day variations are suggested to account for the existence of MEDE at all times of the day.