DIURNAL AND SEASONAL VARIATIONS OF THE LF SKY-WAVE PROPAGATION OVER LONG DISTANCE

This paper presents primary results observed on diurnal and seasonal variations of the 100 kHz Loran-Cfirst-hop sky-wave over a west-east path of about 2880 km from Xinxiang for the time period June 1987-September 1988, and emphatically analysed solar control me-charisms of sky-wave amplitude and phase variations, sky-wave amplitudt drop and interferences.Results of analysis indicate that the relations of the sky-wave amplitude and phase with solar zenith angle x during the daytime are approximately proportional to cos x and P. lnsecx respectively.Successive analysis and explanation for results of observations imply that during the daytime the lower region of the low ionosphere composes of two layers: an upper one (D-layer) which causes the deviative reflection of a sky-wave and a lower one (C-layer) which overlaps partly with an upper layer and causes the non-deviative obsorption of a sky-wave.And it is also found that the C-layer is markedly more intense in summer and autumn than in winter and spring, and that besides the non-deviative obsorption it has caused the marked partial reflection of a sky-wave in summer and autumn