Ionospheric Absorption Over Delhi

Abstract

An automatic method of measuring ionospheric absorption on vertical incidence pulsed transmissions has been developed at the Research Department of All India Radio. The equipment and some preliminary observations have been described earlier. Regular measurements by this recorder were commenced in June 1954 and are still in progress. The present paper deals with the analysis of further measurements made till October 1957.

Absorption was measured on 5 mc./s. every day at midday and at different times on other occasions. The analysis of data reveals the following: (a) Running average of the monthly midday absorption is well correlated with corresponding running average of sunspot numbers; (b) the diurnal variation factor n has been evaluated on some occasions and has been found to lie within the range 0·33–1·13 with more than 80 per cent of values between 0·33 and 0·9; (c) in the evaluation of relaxation time two maxima of absorption, one in the forenoon and the other in the afternoon, have been occasionally observed although there are a few clear instances of only one post-noon maximum; (d) attempt has been made to work out seasonal variation of midday absorption from the measurements. The results described in the paper are rather tentative as measured values of ionospheric absorption spread over a large number of years are required for arriving at definite conclusions.