MUF variability at Haikou, China

By using the ionosonde data at Haikou, China over the time period of 1996-2006, this paper analyses the diurnal and seasonal behaviour of the ionospheric MUF variability at low latitude. Data used in this study are the critical frequency foF2 and the propagation factor M(3000)F2 with hourly interval resolution. Four parameters including upper quartile(Qup), lower quartile(Qlo), monthly inter-quartile(DeltaMUF) and their percentage ratio(DeltaMUF(%)) to the monthly medians are used as quantitative measurement of the MUF variability in diurnal and seasonal study, where in the latter the seasonal averages of these quantities are calculated for winter, equinox and summer, separately. Our study shows: (1)MUF values and their variability are greatly affected by foF2 values and their variability. (2)Instead of falling off after sunset, in high solar active years MUF values remain large until the next early morning. (3)Both MUF Qup and Qlo have the similar trends as those of their corresponding monthly medians. However, the departure of Qup and Qlo from the monthly medians is not symmetric. (4)For the DeltaMUF(%) parameter, the variability is much lower during daytime than nighttime, and the maximum variability appear in the pre-sunrise generally. (5)The seasonal averages of DeltaMUF(%) from 1996 to 2006 are of difference in magnitude in different season. The variation range fluctuates from 18.1% to 49.0% in winter, from 18.4% to 46.2% in equinox and from 17.6% to 39.7% in summer respectively. It is also shown that the seasonal averages of the DeltaMUF(%) is usually smaller in equinox than in winter and summer, except that in pre-sunrise time when they are larger in summer.