TRAVELING IONOSPHERIC DISTURBANCES (TIDS) AT MID-LATITUDES - SOLAR-CYCLE PHASE DEPENDENCE

Faraday observations of total electron content (TEC) at Haifa, Israel (32.87°N, 35.09°E), during periods near the maximum (1980) and minimum (1984) phases of the current solar cycle have yielded information about the structure and variability of the ionosphere during both epochs in general, and about traveling ionospheric disturbances (TIDs) in particular. The TEC is characterized by the large differences in the seasonally dependent absolute values, by the generally occurring spatially confined postsunset secondary maxima during solar maximum which are absent during solar minimum, and by the regularly appearing modulations of the structure due to TIDs. There is a definite seasonal and solar phase dependence in the characteristics of the TIDs. This is expressed in terms of their frequency of occurrence, likely phase of the diurnal variation during which the occurrences take place, their absolute magnitudes, and the time rate of change of these magnitudes.