Seasonal Variation of f_0F_2
Suo Yucheng(China Research Institute of Radiowave Propagation, P. O. Box 138, Xinxiang, Henan, 453003, China).
Based on the observations at eight ionosond stations in China during 1976- 1988(the whole 21st solar activity cycle is contained in this pened), the seasonal variation of foFZ is analyzed. It is pointed out that the seasonal variation of f0F2 during this period exhibited some abnormal characteristics.First.when the mean value of f0F2 in the Period is used the seasonal variation features are as follows:1) During daytime, the maximum of the mean f0F2 occures in spring and autumn 1 2, but is also lower than or near the value in winter 3) Near Sunrise(C3- 06LT), the mean f0F2 value in summer is obviously higher than in winter; 4) DUring night-time,the ) During daytime, the mean f0F2 value in summer is not only lower than the value in apring and autumnmaximum of mean f0F2 in low latitude also occures in spring and autumn, the f0F2 value in summer is lower than in spring and autumn and is even lower than in winter. This result is inconsistent with the well known result of the other authors up to now. The well known result is that for night time foFZ, there is no such phenomenon.On the other hand, the using of mean valuse of f0F2 during the period may balance some features of seasonal variation. So every monthly medium of f0F2 is used rather than its mean value in the pened and the seasonal variation of f0F2 may be refined as follows: 1) For daytime value of f0F2. no matter in solar maximum or in solar minimum,as well as in middle latitude or in low latitude, there is seasonal anomaly .2) In middle latitude, no matter in solar maximum or in solar minimum, there is no seasonal anomaly at all fornight time value of f0F2:3) But in low latitude for solar maximum, ther6 is seasonal anomaly for night time f0F2 value, as if during daytime 4 ) No matter in solar maximum or in solar minimum,as well as in middle latitude or in low latitude I there is no seasonal anomaly at all near sunrise value of f0F2.