Some salient features of the atmosphere observed over the north Bay of Bengal during BOBMEX |
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| Authors: | G S Bhat |
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| Institution: | (1) Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India |
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| Abstract: | This paper describes the near surface characteristics and vertical variations based on the observations made at 17.5‡N and
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
1999. BOBMEX captured both the active and 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, and increased during a weak phase of convection.
It is shown that the latent heat flux at comparable wind speeds was about 25–50% lower over the Bay during BOBMEX compared
to that over the Indian Ocean during other seasons and 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 1-D heat balance model works sometime but not always, and 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 and weak phases of convection. Convective Available Potential Energy of the surface air decreased by 2–3 kJ kg-1 following convection, and recovered in a time period of one or two days. The mid tropospheric relative humidity and water
vapor content, and wind direction show the major changes between the active and weak phases of convection. |
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| Keywords: | Monsoon air-sea coupling tropical convection boundary layer |
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