Seasonal Variations of Global Ionospheric NmF2 and hmF2
The seasonal variations of global ionospheric NmF2 and hmF2 have been analyzed by using the monthly COSMIC ionospheric data from 2006 to 2019 and wavelet analysis method.The results show that the ionospheric NmF2 and hmF2 are significantly different with local time,season and latitude.The ionospheric peak parameters have positive correlation with the solar activity,and their correlation coefficients are above 0.9 and 0.8,respectively.The ionospheric NmF2 at noon exists significantly annual and semiannual variations,especially under the high solar activity conditions.However,the annual vari-ation of ionospheric NmF2 has been mainly observed at nighttime.Meanwhile,the annual variation of ionospheric hmF2 at noon is significant in all years,but almost absent during midnight.Additionally,and the seasonal variations of ionospheric NmF2 and hmF2 in the southern hemisphere are more obvious than that in the northern hemisphere.Additionally,the seasonal variations of ionospheric peak parameters are more significant during high solar activity years.Moreover,there seem to be periodic signals of 25～35 months in the solar activity index and ionospheric peak parameters,but their power spectrum are not greater than 95%significance level,and we thought that the ionosphere would be not affected by the QBO signal.
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