A study of the ionogram derived effective scale height around the ionospheric hmF2

Abstract. The diurnal, seasonal, and solar activity variations of the ionogram derived scale height around the ionospheric F-layer peak (Hm) are statistically analyzed at Wuhan (114.4° E, 30.6° N) and the yearly variations of Hm are also investigated for Wuhan and 12 other stations where Hm data are available. Hm, as a measure of the slope of the topside electron number density profiles, is calculated from the bottomside electron density profiles derived from vertical sounding ionograms using the UMLCAR SAO-Explorer. Results indicate that the value of median Hm increases with increasing solar flux. Hm is highest in summer and lowest in winter during the daytime, while it exhibits a much smaller seasonal variation at night. A common feature presented at these 13 stations is that Hm undergoes a yearly annual variation with a maximum in summer during the daytime. The annual variation becomes much weaker or disappears from late night to pre-sunrise. In addition, a moderate positive correlation is found between Hm with hmF2 and a strong correlation between the bottomside thickness parameter B0 and Hm. The latter provides a new and convenient way for empirical modeling the topside ionospheric shape only from the established B0 parameter set.