4.5 Air-Sea/Land Interaction in Coastal Zone during CASPER-2015

Tuesday, 16 August 2016: 9:30 AM
Lecture Hall (Monona Terrace Community and Convention Center)
Andrey A. Grachev, University of Colorado CIRES / NOAA Earth System Research Laboratory, Boulder, CO; and L. S. Leo, H. J. S. Fernando, C. W. Fairall, B. W. Blomquist, and C. M. Hocut

Measurements of atmospheric turbulence made at the U.S. Army Corps of Engineers Field Research Facility (FRF) located on the Atlantic Ocean near the town of Duck, North Carolina, during the CASPER Program (October-November 2015) are used to study air-sea/land coupling in the FRF coastal zone. Turbulent and mean meteorological data were collected at multiple levels (up to four) on three towers deployed on land at different distances from the shoreline (from the beach in close proximity of the water to the coastal sand dunes) and a fourth tower located at the end of a 560 m-long pier. Furthermore, eddy covariance data and lidar observations collected in the coastal zone aboard R/V Atlantic Explorer are discussed in relation to FRF coastal turbulence measurements. The data allow studies of temporal and spatial variations of offshore and onshore coastal atmospheric boundary layer flows in detail. The data also permit comparison of turbulent fluxes and turbulence statistics (e.g., turbulent kinetic energy, skewness, and kurtosis) as well as different scaling laws for turbulent mixing over different footprints, including sea surface and inland areas. The ocean has a very large heat capacity and relatively smooth surface (compared to land), which stores the heat for longer times and permits turbulent mixing to larger depths, thus impacting the diurnal cycle. In contrast, dry land areas are aerodynamically rough in general and have low heat storage capacity, thus allowing a stronger diurnal cycle of the sensible heat flux. According to our data, the drag coefficient, Bowen ratio, and diurnal variation of air temperature and sensible heat flux can be considered as indicators for different types of surface footprints. It was found that the drag coefficient and the Bowen ratio over aerodynamically rough land footprint areas increase dramatically and can be about an order of magnitude larger than that over a smooth sea surface footprint. With onshore flow, the internal boundary layer in the coastal zone may be stable or (mostly) unstable, and vary dramatically at the coastal land-surface discontinuity. With the offshore flow of generally warm air over cool sea surface, a stable internal boundary layer develops over the ocean surface downstream from the coast.
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