Diurnal and seasonal variation of the ionogram-derived scale height at the F2 peak Original Research Article

The Chapman scale height HT at F2 peak, which can be used to construct a topside electron density profile model, is deduced from ground-based ionograms. In this paper, HT values obtained from ionograms recorded at the low latitude station Hainan (19.4°N, 109.0°E), China is used to study its diurnal, seasonal, and solar activity dependence. The correlations between HT and the F2 peak parameters foF2 and hmF2, the best-fitted IRI-parameter B0, and the ionospheric slab thickness τ are also studied. Data used for the present study covered a 2-year time period from March 2002 to February 2004. The present study showed that: (1) Diurnal course of the HT has two peaks, with the main one occurring at daytime hours around noontime and the other occurring before sunrise. The pre-sunrise peak is most obvious for winter compared with that for summer and equinox. The minimum values of HT occur around midnight and sunrise hours. The time of occurrence of the sunrise minimum is earliest for summer and latest for winter. (2) HT shows a clear annual variation with largest daytime values occurring in summer and smallest values in winter. (3) HT shows strong solar activity dependence, with the daytime value of HT decreasing with decreasing solar activity. (4) HT is strongly correlated with the bottomside F2 layer thickness parameter B0 and the ionospheric slab thickness τ. The high correlation between HT and B0 parameter suggests the possibility to construct the topside electron density profile model based on the B0 parameter previously established for the International Reference Ionosphere.