Variations of the ionospheric F2 layer critical frequency at Zhongshan Station, Antarctica

With the statistical analysis of the monthly medians from 1995 to 2002 of the DPS-4 ionospheric sounder at Zhongshan Station, Antarctica, main features of the ionospheric critical frequency (f_oF_2) are revealed. The result shows that the frequency f_oF_2 has obvious diurnal and annual variations. There is a “magnetic noon anomaly of the diurnal variation. The “winter anomaly of the annual variation does not occur at local noon at solar minimum, while the “semi-annual anomaly occurs at solar maximum, which means f_oF_2 is larger at equinoxes than at solstices. The physical mechanisms of these phenomena are discussed according to ionization of solar radiation, the driven factors from magnetosphere and variations of neutral components of the atmosphere at the location of Zhongshan Station.