Ionosphere over Calcutta: Solar half-cycle January 1945–June 1950

Ionospheric records made at Calcutta during the solar half cycle January 1945 to June 1950 have been analysed with a view to determine the values of the following ionospheric parameters: 1. (1) rate of electron production, 2. (2) temperature, 3. (3) effective coefficient of recombination. The value of the terrestrial magnetic field at the average height of region F2 has also been determined. The following are the results obtained: 1. (1) For Region F2 the rate of electron production is highest after sunrise and before sunset and lowest during midday (400/cm3/sec after sunrise and before sunset, and 60/cm3/sec during midday). The same is also true to a lesser extent for Region E. Exceptions to these types of variation occur only during winter (specially during the period of low solar activity) when the rate is more nearly normal. 2. (2) The seasonal variation in temperature is most marked for region F2 (varies from 700° K in winter to 1200° K in summer during high solar activity and from 500° K in winter to 900° K in summer during low solar activity). It is shown that the total variation is not due entirely to the direct heating effect of the sun, but partly to the presence of a rising temperature gradient in the F2 layer and the transport of the F2 layer as a whole from a lower to a higher region. 3. (3) The effective coefficient of recombination undergoes seasonal and diurnal variation for both E and F2 regions. For Region E, the variation depends only on temperature: for Region F2 on temperature and on pressure. Representative values of the coefficient are 1.5 × 10-10 cm3/sec in winter and 6 × 10-11 cm3/sec in summer for Region F2 and 2 × 10-9 cm3/sec in winter and 1 × 10-9 cm3/sec in summer for Region E. 4. (4) The value of the magnetic field at the average height of Region F2 agrees with that expected from the inverse cube law (0.36 Gauss). The magnetic field also shows a seasonal variation. Graphs showing the variations of the different quantities studied are given. A graph depicting the solar activity during the period (Zurich sunspot number) is also given