Study of Monsoon Rainfall in Relation to the Movement of Upper Air Anticyclone

Abstract

Using the Constant Pressure (C.P) chart upper air anticyclonic axis position at 200 and 300 hPa levels were studied. The anticyclonic axis position has been drawn on C.P. chart and location of the axis has been determined along 850, 900 and 950 E longitude. Using these locations a best-fitted straight line have been fitted. The latitudes of the best fitted straight line w.r.t. the particular stations have been determined at regular basis in the monsoon season of 1998, 2000, 2001 and 2002. The anomalies of the axis positions have been also investigated from the monthly mean position. Then we have tried to identify how the monsoon rainfall is correlated with the movement of the upper air anticyclonic axis position. In this study we have considered 10 stations of different quadrant covering whole Bangladesh. We have found from the analysis that rainfall occurred over Dhaka, Barisal, Chitlagong, Comilla, Dinajpur, Khulna, Mymensingh, Rajshahi, Seemangal and Syihet station when the upper air anticyclonic axis of 200 and 300 hPa levels were close to the stations. In the 2 half of July and 1t half of August the anticyclonic axis was away from the stations but rainfall occurred over the stations at that duration. When the anticyclonic axis of 200 and 300 hPa levels moved continuously from north to south or south to north rainfall occurred over all of the stations either in that duration or at the end of that duration in the monsoon season. In the 15t half of June the anomalies of anticyclonic axis position was below the mean position and in the 2 half the axis was above the mean position for 200 and 300 hPa levels. In July and August it was oscillatory about the mean position and in September it was above the mean position during 1St half and below the mean position during 2 half with some exceptions for both the levels. The average rainfall of 34 meteorological stations of Bangladesh has been computed on regular basis during the monsoon season of 1998, 2000, 2001 and 2002. The correlation co-efficient between the daily average rainfall in the monsoon season and the upper air anticyclonic axis position have been studied and we observed that the correlation co-efficient between them is not significant for 200 and 300 hPa levels.