Boundary Layer Quasi-equilibrium and Tropical Atmospheric Circulations

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9616290 Raymond, New Mexico Institute of Mining and Technology "Boundary Layer Quasi-equilibrium and Tropical Atmospheric Circulations" Dr. Raymond will explore the idea that moist convection over the tropical oceans is controlled by the entropy balance of the sub-cloud layer of the atmosphere. This hypothesis, known as the boundary layer quasi- equilibrium (BLQ), will be examined through a series of modeling experiments with a recently developed cumulus ensemble model and with the principal investigator's equatorial beta plan primitive equation model as well as through analysis of TOGA COARE data. Dr. Raymond also will explore the consequences of this hypothesis for tropical atmospheric circulations in general. Simply stated, this hypothesis asserts that the boundary or sub-cloud layer rapidly adjusts to the inflow and outflow of moist entropy in such a way that inflow balances outflow on time scales of half a day or greater. In the moist tropics, the primary elements in this process are sea-air fluxes and convective and mesoscale downdrafts from moist convection, although dry entrainment into the boundary layer can be important in instances where very dry air exists just above the boundary layer. The net result is that sea-air fluxes (and in some case, dry entrainment) exert a strong control on convective activity. In pursing this hypothesis, Dr. Raymond will focus on three issues: (1) the scales of motion over which the BLQ applies, (2) how variations in middle level atmospheric moisture, wind-shear and related conditions affect the ratio of updrafts and downdrafts and thus the boundary layer balance, and (3) the implications of BLQ with respect to large-scale tropical circulations. This work has important implications for the treatment of convection in global climate and weather models.