Solar tides in the ionosphere over Calcutta

The ionospheric data for the F2-region over Calcutta for the period January 1946 to January 1950 are analysed with a view to determine the amplitude and phase of solar tidal drifts (both semi-diurnal and seasonal), to explain the anomalous ionization changes of F2-region and to determine the values of the recombination coefficient in summer and in winter. MARTYNS mathematical analysis on ionospheric tides has been extended for this purpose. It is found that: 1. (i) The resultant drift velocity at Calcutta is 12 km/hr in both summer and winter, and 17 km/hr in the equinoxes, being maximum downwards at 1630 in summer, at 1500 in the equinoxes and at 1330 in winter; 2. (ii) the observed anomalous variations of F2 ionization, both in night and in day-time, are explained taking into account the effects of both recombination and tidal drifts; 3. (iii) the calculated values of the coefficient of recombination are all of the order of 10-11 cm3/sec