The composite structure of the monsoon depression



A composite three dimensional structure of the monsoon depression has been constructed using five monsoon depression cases of 1973. The parameters considered for compositing are wind components, temperature, relative humidity, surface pressure, cloud cover and precipitation. The distributions of these parameters are obtained with respect to the depression center as origin. The results indicate that the depression is an intense low pressure system with a central pressure of 990 mb. The associated circulation is very vigorous. Strongest winds of about 50 kts are noted in the southwest. The analyses of the pressure and wind fields suggest that the horizontal scale of the depression is about 1500 km. The field of temperature anomaly clearly brings out the cold core structure of the depression. The precipitation pattern shows that the rainfall rates exceeding 120 mm in 24 hrs occur to the west of the depression.

The vertical cross-sections through the center of the depression of horizontal wind components indicate that the depression is confined to the lower troposphere from the surface up to 400 mb. The region ahead of the depression is characterized by strong cyclonic vorticity, convergence and upward motion. Relatively weak anticyclonic vorticity, divergence and subsidence are noted behind the depression.