Journal of the Marine Biological Association of India

Volume 15 Issue 1

Forecasting the onset of monsoon over Kerala with the help of satellite cloud pictures.

R. Jambunathan and K. Ramamurthy

Since the launching of the Operational Weather Satellites carrying the APT (Automatic Picture Transmission) system in the beginning of 1966, the actual cloud photographs over India and the adjoining sea areas are being regularly received through the APT Ground Station at Bombay. Utilising these cloud pictures, the cloud-cover and its progress over south Arabian Sea and the adjoining equatorial region during May and June were examined for the years 1967 and 1968 with a view to study the advance of the southwest monsoon into Kerala. The results of this study have been published in the Forecasting Manual of the India Meteorological Department. The study revealed that there is a progression of cloud maximum northward from the equatorial region and the mean clouding over the Arabian Sea in the latitude of Kerala (7.5° N to 10°N) reaches2—3 oktas about a week prior to the onset of the monsoon over Kerala. This result, though based on two years' data, appears to be useful from the point of view of medium range forecasting of the onset of monsoon over Kerala. As the network of surface and upper air observatories is sparse and ships' observations generally few over south Arabian Sea and the adjoining equatorial region and as the available methods of forecasting the onset of the monsoon over Kerala using the conventional data have not been quite successful, the clouds covering vast areas of the south Arabian Sea and the adjoining equatorial region as revealed by the Satellite Photographs seem to be a fairly reliable tool for this purpose. Hence a study of the Satellite Cloud Pictures over the Arabian Sea for three more years, viz., 1966, 1969 and 1970 has been made and the results are presented in this paper. The results confirm the earlier findings. In the opinion of the authors, a study of the satellite cloud pictures as outlined in this paper can serve as a reasonably reliable guide for forecasting the onset of monsoon over Kerala about a week ahead.

Date : 31-08-1973