Some salient features of the atmosphere observed over the north Bay of Bengal during BOBMEX

Abstract

This paper describes the near surface characteristics; vertical variations based on the observations made at 7.5° N; 89° E from ORV Sagar Kanya in the north Bay of Bengal during the Bay of Bengal Monsoon Experiment (BOBMEX) carried out in July-August 999. BOBMEX captured both the active; weak phases of convection. SST remained above the convection threshold throughout the BOBMEX. While the response of the SST to atmospheric forcing was clearly observed; the response of the atmosphere to SST changes was not clear. SST decreased during periods of large scale precipitation; increased during a weak phase of convection. It is shown that the latent heat flux at comparable wind speeds was about 5-50% lower over the Bay during BOBMEX compared to that over the Indian Ocean during other seasons; tropical west Pacific. On the other hand; the largest variations in the surface daily net heat flux are observed over the Bay during BOBMEX. SST predicted using observed surface fluxes showed that -D heat balance model works sometime but not always; horizontal advection is important. The high resolution Vaisala radiosondes launched during BOBMEX could clearly bring out the changes in the vertical structure of the atmosphere between active; weak phases of convection. Convective Available Potential Energy of the surface air decreased by - kJ kg^-1 following convection; recovered in a time period of one or two days. The mid tropospheric relative humidity; water vapor content; wind direction show the major changes between the active; weak phases of convection