5:15 PM - 6:45 PM
[AAS03-P06] Quantification of boundary-layer moist static energy budget processes in tropical oceanic deep convective regime
Keywords:Cumulus convection, Boundary-layer quasi equilibrium, Shipborne observation, Indo-Pacific warm pool
Over the Indo-Pacific warm pool, vigorous deep cumulus convection plays a significant role in activity of various large-scale atmospheric disturbances. Intensity of the convection largely depends on thermodynamic conditions in the atmospheric boundary layer (BL), which are often measured by moist static energy (MSE). Therefore, it seems important to examine budget processes of BL MSE. In the BL quasi-equilibrium framework, we can expect that increase of BL MSE due to surface turbulent heat flux is balanced with its decrease by three processes: entrainment of free-tropospheric air caused by BL turbulence, convective downdraft due to evaporation and loading of falling raindrops, and radiative cooling. While the radiative cooling is considered to play only a minor role, which of the other two processes contribute the major role is still an open question. This study quantifies contribution of these two processes through analysis of in situ observation data obtained by research vessel Mirai of JAMSTEC during her station observation periods in seven research cruises over the warm pool (nearly 200 days in total). It is found that both processes play nonnegligible roles in BL MSE budget, and the contribution of the entrainment is generally larger than that of the convective downdraft in a realistic range of prescribed radiative cooling rate. The contribution of convective downdraft correlates well with convective activity around the vessel, and the MSE flux by this process per unit amount of precipitation can roughly be estimated. On the other hand, the contribution of the entrainment correlates well with surface wind speed, which might imply that intensity of BL turbulence is largely controlled by wind.