南极中山站电离层F2层临界频率变化特征

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

对南极中山站数字式电离层测高仪1995～2002年观测数据的月中值进行了统计分析，揭示了中山站电离层F2层临界频率（foF2）的主要特征：foF2存在明显的日变化和年变化；日变化存在“磁中午异常”现象；年变化中中午foF2在太阳活动低年不出现“冬季异常”，在太阳活动高年出现“半年异常”，即两分点高于两至点．本文结合中山站所处的地理位置，考虑太阳辐射电离、磁层的驱动和中性大气成分变化等因素，分析了这些现象的产生机理．

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 oF2 ） are revealed. The result shows that the frequency foF2 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 foF2 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.