Seasonal Effects in Lunar Tides in Midday Critical Frequency of the F₂-Layer of the Ionosphere

ABSTRACT

The paper describes the lunar tides in midday values of f₀F₂ at a large number of ionospheric stations during different seasons of the year of low solar activity. The phase of lunar tide is found to vary with season by about 2–3 lunar hours at subtropical latitudes and by less than two hours at equatorial latitudes. The reversal of phase between the equatorial and subtropical latitudes is most prominent during December solstices and almost absent during June solstices. The amplitudes show a sharp maximum over the magnetic equator and broad maxima at subtropical latitude most distinctly during December solstices and very feebly during June solstices. Thus the lunar tidal effects in f₀F₂ are in general stronger during December than June solstice indicating a strong annual effect. The seasonal variation of tidal amplitudes are very similar to that of average f₀F₂ and similar agencies should be producing both the effects.