Midlatitude summer nighttime anomaly in NmF2 according to the data of vertical sounding in Alma-Ata

The morphology of the midlatitude summer nighttime anomaly in the diurnal behavior of the electron concentration maximum in the F2 layer in various seasons and at various solar activity levels was studied with the use of vertical sounding data in Almaty in 1999, 2008, 2011, and 2012. It was shown that the anomaly is manifested most distinctly in the summer months (June–August) and disappears in the equinox months (March, September). The maximum value of the electron concentration falls on the solar zenith angles, which correspond to the cessation of the arrival of ionizing radiation at the heights of the F2-layer maximum. The anomaly is clearly manifested in the solar activity minimum and barely seen in the maximum. It was shown that the summer anomaly parameters at the boundary of the northeastern Asia (Almaty, 76°55′ E) insignificantly change as compared to the parameters of its center (Japan, 130° E). Mechanisms of anomaly formation, as well as of its diurnal and seasonal behavior, are discussed.