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Boundary Layers and Interfacial Interactions

Focus: To improve our understanding of oceanic and atmospheric boundary layers, and the exchanges that occur across the surface/atmosphere and the boundary layer/free atmosphere interfaces.

We now have a good understanding of the clear convective planetary boundary layer (PBL) over homogeneous terrain. But most horizontal heterogeneities introduce substantial additional complexities, for example:

* Waves modify the oceanic PBL structure in ways that depend on their amplitude, speed and direction;
* Clouds within or emanating from the PBL can markedly alter its structure;
* Surface heterogeneities, such as spatial variations of soil types, soil moisture, vegetation, and topography, lead to significant horizontal variations in the contributors to the surface energy budget, and thus PBL structure; and,
* Stably-stratified PBLs remain a largely unresolved problem because of their intermittent turbulence and sensitivity to gravity wave effects. This leaves us with a broad range of PBLs whose structures are not well quantified, which we plan to investigate under this research program.

One of the most climatologically important PBL cloud types is marine stratocumulus. Small changes in its fractional cloud cover or microphysical properties can markedly alter the amount of solar radiation input to the ocean surface, which has both weather and climate implications. Two important processes that control stratocumulus evolution are entrainment and drizzle and evidence is accumulating that drizzle is associated with a characteristic mesoscale pattern of open cells. We are studying the role of these processes both via observations obtained from the Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) and by large-eddy simulations (LES). Our goal is to develop better understanding of the fundamental processes and use this to improve parameterizations for larger scale models.

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