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Interaction of the Lower Atmosphere and Upper Ocean

The proposed research is a joint project between UCLA and NCAR. The research is for process modeling of fine-scale circulations in the lower atmosphere and upper ocean in the northwest Tropical Atlantic as part of the U.S. Atlantic Trade-wind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) and the European EUERC4A-OA Projects. It is in response to NOAA’s Climate Variability and Predictability (CVP) Program: Competition 2: CVP-Observing and Understanding Upper-Ocean Processes and Shallow Convection in the Tropical Atlantic Ocean. The guiding hypothesis of the research is that surface heterogeneities in oceanic temperature (SST) and currents induce heterogeneities in the air-sea fluxes of heat, moisture, and momentum, which in turn modulate the mesoscale and submesoscale circulations in the oceanic surface layer and atmospheric boundary layer. The source of the heterogeneity is oceanic mesoscale eddies and submesoscale fronts.
We will use two modeling approaches to elucidate the interaction between the lower atmosphere and the upper ocean: idealized flow configurations in a Large Eddy Simulations (LESs) that resolve the boundary-layer turbulence (led by NCAR) and “realistic” down-scaled coupled simulations using the Weather Research and Forecast (WRF) and the Regional Oceanic Modeling System (ROMS) with parameterized vertical fluxes due to boundary-layer turbulence (led by UCLA). The phenomena arising in these separate, different-scale simulations will be used to inform each other to develop, by bootstrapping, a better process understanding across the interacting range of scales from boundary-layer turbulence to the mesoscale winds and currents. We will design a sequence of studies that explore, in the context of Tropical Atlantic phenomena, how submeoscacle currents interact with the boundary layer turbulence in the ocean, how surface gradients in SST and currents interact with the boundary layer turbulence in the atmosphere, how the resulting secondary circulations extend vertically through the upper ocean and lower atmosphere, and how the Thermal and Current Feedbacks develop mesoscale and submesoscale correlations across the air-sea interface, even reaching into the shallow cloud layer above. The key methodologies are the massively parallel LES code developed over many years at NCAR, including surface wave dynamical influences in both the air and water, and the ROMS circulation model developed at UCLA that also includes surface wave interactions and allows multiple levels of grid nesting conveying larger scale influences down to finer scale circulations, in particular allowing very high resolution studies of submesoscale phenomena shaped by the encompassing mesoscale eddies and regional currents.
Because of the extensive international field measurements planned, we would work closely with the observing groups, especially those that have fine-scale sampling in both time and at least one horizontal coordinate. The intent is to combine the relatively more complete information from model simulations with the measured reality, for the better interpretation of both, and to establish the importance of surface heterogeneity in climate outcomes. To this end we intend to work closely with both the European and American experimental teams.
This research enhances our process-level understanding of the climate system through observation, modeling, analysis, and field studies. This vital knowledge is needed to improve climate models and predictions so that scientists and society can better anticipate the impacts of future climate variability and change.

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