Entrainment, Decoupling, and Vertical Transport in the Marine Stratocumulus Cloud Deck

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Marine stratocumulus clouds cover significant areas of the ocean and act to cool the planet by reflecting incoming sunlight. The processes behind these low clouds are not well simulated by weather or climate models. This award will allow researchers to analyze data that was collected in a prior field campaign so that they can study the movement of air and moisture within marine stratocumulus clouds. The result will be a better understanding of the clouds and an improved ability to model their formation, dissipation, and impacts. One main impact of the research will be on weather forecasting with a focus on low clouds and fog, which are hazards for the aviation industry. The work will also help to improve climate models. Training and diversity impacts will be provided through the incorporation of students into the research plan.The research team will conduct an analysis of lidar, radar and sounding data from the 2008 VAMOS Ocean Cloud Atmosphere Land Study (VOCALS) to better understand the processes that control the structure, transitions, and radiative properties of stratocumulus clouds. The researchers note that vertical mixing is poorly observed in stratocumulus cloud top entrainment, in cumulus updrafts rising into stratocumulus, and in evaporative downdrafts. Conceptual and numerical models of these phenomena have only been evaluated by their effects on external phenomena, rather than how well the models represent the actual internal processes themselves. Three scientific objectives are identified that will lead to a better description and understanding of entrainment, decoupling, and coherent updraft and downdraft fluxes: 1) Relating entrainment to the strength of turbulence in the stratocumulus cloud and documenting diurnal variations of turbulence and its transport due to variation of buoyancy flux at cloud top, 2) Documenting the structure and evolution of turbulence leading to decoupling between the stratocumulus cloud and surface mixed layer, and analyzing both diurnal decoupling driven by the cycle of solar radiation, and decoupling associated with large-scale cold advection over warm SST, and 3) quantifying mass transports due to cumulus updrafts and downdrafts generated by negative buoyancy from cloud and drizzle evaporation, and attributing the observed distributions of vertical velocity to turbulence strength, decoupling, cumulus clouds, and drizzle.