Thermospheric parameters contribution to the formation of Yakutsk F(2)-layer diurnal summer time anomaly

The role of thermospheric neutral composition in the formation of the Yakutsk diurnal summer time foF(2) anomaly is analyzed. Ionospheric stations inside and outside the anomaly area are considered. The effect of neutral composition in foF(2) is the most noticeable around noontime hours. The difference between observed noontime foF(2) in two areas is significant at the 99.9% confidence level both for monthly median and individual days. The inferred from ionosonde observations and Swarm neutral gas density thermospheric parameters indicate a significant difference between two areas. The inferred exospheric temperature, Tex at Magadan (inside the anomaly area) is significantly larger than Tex at Tunguska (outside the anomaly area). On the contrary, the inferred atomic oxygen [O] at Tunguska is significantly larger than at Magadan. Different [O] abundance in the two areas is the main reason of the observed difference in noontime foF(2) values. Vertical plasma drift depending on magnetic declination, D is the only process responsible for the difference between nighttime foF(2) at Tunguska and Magadan. A possible mechanism of the revealed difference in thermospheric parameters inside and outside the anomaly area is discussed.