Radon Daughter's Radioactivity Levels over the Arabian Sea as Indicators of Air Mass Mixing

Abstract

Measurements on radon daughter's activities over the Arabian Sea were carried out during the period 19 May to 9 July, 1973, under the joint Indo-USSR MONEX-73 project. The data were collected on board the ships of the Indian Navy cruising between 19?21°N within longitudes 60?73°E and the two USSR vessels Okean and Prilive cruising between latitudes 0?10°N and 10?18°N, respectively. The results show that there is a significant increase in radon daughter's activity at about 19?21°N, the average level being of the order of about 8 pCi m?3 as compared to 1?2 pCi m?3 at lower latitudes. This is explained, on the basis of synoptic charts and available sounding data, as being due to the normal wind and pressure pattern prevailing during the monsoon months which results in the transport of continental air from Arabia and Pakistan and its mixing with the maritime monsoon air mass of Southern Hemispheric origin. The significant increase in radon activity on some days of the cruise was mainly due either to the existence of disturbances like depressions, cyclonic storms, etc., over the north Arabian sea, or to the passage of western disturbances at relatively lower latitudes (along ?25°N) and their associated circulation patterns. These phenomena favor significant transport of continental air from the north and west. The mixing of this air mass with air masses of low radon concentrations results in increasing the average radon levels from 1 to 8 pCi m?3.