太阳活动低年南极中山站电离层F层的平均特性

根据１９９５—１９９７年３年中山站数字式电离层测高仪的数据，分析了中山站不同季 节Ｆ层的临频变化特点．中山站夏季主要受太阳光光化电离的影响，Ｆ层临频随地方时的变 化与中纬台站相似；两分季，极隙区软电子沉降的作用显著，Ｆ层临频随磁地方时而变化，有 较明显的磁中午现象．冬季，太阳全天处于地平线以下，中山站Ｆ层临频的变化主要受极隙 区软电子沉降和极区等离子体漂移的影响，其峰值变化处于碰中午和地方时中午之间．中山 站夏季全天都能观测到Ｆ层的存在；两分季Ｆ层在地方时子夜附近的出现率较少；冬季月份 在磁地方时午后和子夜Ｆ层出现率明显减少，这可能与南半球冬季的高纬槽和极洞有关．对 Ｆ层不均匀区的分析认为，中山站在ｔ_(ＬＴ)为１６：００左右处于极光带赤道侧，２０：００左右进入极盖 区。

OVERALL PROPERTIES OF F REGION AROUND SOLAR MINIMUM AT ZHONGSHAN STATION,ANTARCTICA

Based on the monthly data of DPS--4 in 1995-- 1997, we analyze the seasonal properties of F region at Zhongshan Station. In summer, F region ionization is dominated by the solar ultraviolet radiation. Similar to the phenomenon of midlatitude, the f_0 F_2 varies with local time; In equinox seasons, soft electron precipitation from the cusp / cleft region seems apparent. f_0 F_2 chages with MLT, and shows the magnetic noon phenomenon. In winter, solar radiation is less effective to F region ionization. Instead, F region is affected by particle precipitation from cusp / cleft region as well as ionospheric plasma convection, and so the diurnal variation of critical frequency lies between LT and MLT; F region in summer and equinox are more stable. However, in winter the occurrences of F region near afternoon cusp and midnight are much less. We think this phenomenon is caused by the high-latitude ionospheric trough and polar hole; After further analysis of F region spread, we find that the duration of aurora oval passing over the Zhongshan Station t_(TL) is from 16:00 to 20:00h.