Large-eddy simulations are used to investigate the effects of coastal topography and atmospheric stratification on the coastal marine atmospheric surface layer at the Field Research Facility in Duck, North Carolina, USA. Field measurements obtained from the CASPER-EAST intensive field campaign in autumn 2015 are used to determine the inlet and lower boundary conditions. The simulations are performed using the in-house Virtual Flow Simulator code, with the simulated mean streamwise velocity component, mean temperature, Reynolds shear stress, and turbulent heat flux, shown to be in good agreement with measurements. In the coastal area, the complex coastal topography leads to an enhancement of the Reynolds shear stress for both onshore and offshore flows, while the effect of atmospheric stratification on the momentum transfer is less significant than the topography. In contrast to the momentum flux, the heat flux is influenced by both the coastal topography and stratification. For onshore flow and stable stratification, the heat flux is significantly increased near the sand dune due to the enhanced turbulence and vertical temperature gradient. For onshore flow and unstable stratification, the strong turbulent mixing tends to enhance the heat flux, but is suppressed by the reduced vertical temperature gradient, such that the magnitude of the turbulent heat flux remains almost unchanged in comparison with the upstream flow. For offshore flow in both stable and unstable stratification, the heat flux is enhanced due to the flow separation at the sand dune.
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Acknowledgements This research is supported by the Office of Naval Research as part of the Coastal Air– Sea Process and Electromagnetic Research (CASPER) project under its Multidisciplinary University Research Initiative (MURI) program managed by Dr. Daniel Eleuterio and Dr. Steven Russell. The simulations in this work used the computational resources available during the Coastal Land–Air–Sea Interactions (CLASI) project sponsored by Office of Naval Research managed by Dr. Reginald Beach.
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- Atmospheric surface layer
- Coastal area
- Coastal topography
- Flow separation
- Large-eddy simulation