STUDY OF THE STRUCTURE OF A MONSOON DEPRESSION OVER THE BAY OF BENGAL DURING SUMMER MONEX

Based on the data gathered during the Summer MONEX over the Bay of Bengal in July, 1979, a detailed observational study of the structure of a monsoon depression during the period of 3-8, July has been made. It has been revealed that the early disturbance of this depression was a mid-tropospheric cyclone. The subsequent rapid development was due mainly to the barotropic instability process of the basic zonal and meridional airflows.The cyclonic circulation of the depression extended in vertical upward to 500-400 mb level. Prior to the formation of the depression, the extremely strong westerly and northerly winds at the lower and middle levels, reaching the intensity of the low-level jet (22 m/s and 18.5 m/s, respectively), were observed. Post to the formation of the depression, a strong wind ring at the radius of 300-350 km from the depression center encircled the depression, with the wind maximum being at 850 mb. During this period, the maximum of the positive vorticity was of the magnitude of order of 10-4/s. The warm core at 400-300 mb was very remarkable. Finally, intrusion of the dry air over the depression may be an important factor leading to the weakening of the depression.