Seasonal variation of the lunar tidal effects in the F<SUB>2</SUB> layer of the ionosphere over Indian stations

The lunar semi-diurnal oscillations in the midday values of the critical frequency (&#402;0F2) and the height of maximum electron density (hpF2) of the F2 layer are computed for all Indian ionospheric stations separately for each season of the year. The amplitude of oscillation in &#402;0F2 is found to be larger in winter than in summer at each of the stations. There is a reversal in the phase of the oscillation in &#402;0F2 between the equatorial and tropical latitudes and this is most evident in the winter months and is almost absent in summer. The annual average oscillation in &#402;0F2 is in agreement with that found in a previous paper (Rastogi, 1961). The phase has a large seasonal variation of about 180&#176; at an equatorial or a tropical latitude station. The phase and amplitude of the lunar tide in hpF2 do not vary significantly with latitude or with season