• Monsoonal atmosphere is somewhat unique compared to other warm tropical oceans in the sense that sea-air temperature and specific humidity differences are significantly lower over the North Bay, which combine to yield a 30-50% lower surface latent heat flux at a given wind speed.

• The recovery time scale of the atmospheric mixed layer was 1 to 2 days following a convective disturbance.

3. A study of the structure of the convective atmosphere over the Bay of Bengal associated with monsoon depressions during BOBMEX- 99

U.C. Mohanty, N.V. Sam, S. Das and A.N.V. Satyanarayana, Centre of Atmospheric Sciences, Indian Institute of Technology, New Delhi

• An attempt was made to study the structure of the convective atmosphere over the Bay of Bengal associated with monsoon depressions during BOBMEX-99. For this purpose a semi-prognostic cloud model was employed. This study showed the variation in the kinetic and convective parameters during the transition from suppressed to active period of convection.

4. Observed daily large-scale rainfall patterns during BOBMEX-99.

A.K. Mitra, M. Dasgupta, R.K. Paliwal & S.V. Singh, NCMRWF, New Delhi.

• For the whole BOBMEX-99 period daily large-scale rainfall maps were prepared. These were prepared by merging rain gauge values with the rainfall derived from INSAT IR data. The analysis was able to capture all the important rainfall events around India for the monsoon flow. Composite of active/break phases, intra-seasonal variability and time series of rainfall over the Bay of Bengal was examined. Total rainfall for August-99 period was compared with the Xie & Ankin rainfall maps.

• The global T80 model’s rainfall forecasts for the BOBMEX period were examined.

• Under ‘Indian Climate Research Programme’, we intend to prepare such daily rainfall maps continuously for longer period.

5. Intra-seasonal variability of the low level Jet stream of 1998, 1999 and 1979 – 1983

P.V. Joseph, S. Siji kumar and V. Sajith, University of Cochin, Kochi.

• Monsoon Low Level Jet stream (LLJ) over India had considerable north-south movement in association with the 30-50 day oscillation of the monsoon’s Maximum Cloud Zone (MCZ). There were two resting positions for MCZ and LLJ one (A) between latitudes 5°S and 10° N and the other (B) between 15°N and 25°N. Area ‘A’ where MCZ bands took birth in each 30-50 day cycle had a warm tongue in the upper ocean with cold upwelled waters to its north. This area may be studied in a field experiment to understand the 30-50 day oscillation of MCZ, LLJ and the monsoon.