Mid-latitude Summer Evening Anomaly (MSEA) in F2 layer electron density and Total Electron Content at solar minimum

This paper deals with study of the ionospheric Mid-latitude Summer Evening Anomaly (MSEA) in the F2 layer peak electron density (NmF2) in the Northern Hemisphere and its manifestation in the Total Electron Content (TEC) during the solar activity minimum. The MSEA is identified as an anomaly in the NmF2 diurnal variations when the evening time NmF2 values exceed the daytime NmF2 over a mid-latitude station. For this investigation we used the Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) and observation data of the NmF2 and TEC over Irkutsk (52.3°N,104.3°E) and Kaliningrad (54.6°N,20.0°E). We demonstrate that the MSEA is a purely summer feature in the NmF2 diurnal variations. MSEA is found in TEC, but it is less pronounced and it is observed at the earlier hours in comparison with the MSEA appearance in NmF2. The MSEA appearance in TEC is much more distinct over Irkutsk than Kaliningrad. The later sunset and the upward field aligned plasma transport by the thermospheric winds are the main drivers and sources for the MSEA formation. The ratio n(O)/n(N2) contributes also to the MSEA formation. In summer the diurnal variation in the electron content of the altitudinal range near the F2 layer peak height (175–450km) almost fully determines the diurnal variation and therefore the MSEA formation in TEC. The significant diurnal variation in the electron content of the topside ionosphere and plasmasphere (450–20,200km) fully coincides with the maxima and minima in the diurnal variations in TEC and the F2 region ionospheric electron content. The contribution of the topside ionosphere and plasmasphere in TEC in the summer of 2009 exceeds 40%. The lower ionosphere (80–175km) contribution to TEC has a daytime maximum that does not exceed 10%.