| Drizzle is commonly observed in the stratocumulus-topped boundary layers. Yet, the clear interpretation of how it interacts with the boundary-layer turbulence is lacking. In attempt to bridge the existing gap, this dissertation investigates the role of drizzle in the mesoscale structure and dynamics of the flow in the drizzling stratocumulus-topped boundary layer. Large-eddy simulations on heretofore unimaginably large domains are utilized. To study the structure, a bulk microphysical parameterization is introduced, while for the analysis of dynamics, a horizontally uniform forcing is imposed.; Precipitating stratocumulus are shown to be realistically represented in the simulations. In particular, tendency of the boundary layer to transition to more cumulus-coupled circulation, with locally elevated cloud tops and patches of anomalous sub-cloud equivalent potential temperature in the vicinity of precipitating clouds are captured. The observed tendency for precipitation to be associated with the emergence of a more marked mesoscale circulation and a general reduction in cloudiness is also captured. Moreover, it is shown that the evaporation of precipitation is critical to the observed flow transition, and that the sub-cloud circulations (cold pools) that originate in such a process appear to play a vital role in shaping the structure of both the sub-cloud layer and regions of new convection. Furthermore, localized interactions of drizzle and boundary-layer flow are shown to lead to the development of the mesoscale flow and cloud organization, where the cloud organization follows the flow organization. It is also confirmed that the energetics and reorganization of the flow toward the larger scales in the drizzling STBL are driven by the budget of liquid-water potential temperature. |
