Effects of the Surface and Atmospheric Stability on the Integral Length Scale at a Coastal Site
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We analyze the effects of surface heterogeneity and atmosperic stability on the velocity integral scale at La Paloma, a coastal location in Uruguay, using measurements from three three-dimensional 32-Hz ultrasonic anemometers at heights of 11 m, 40 m, and 66 m for the period December 2016–April 2017. The vertical profiles of heat and momentum fluxes indicate that flow from the sea develops an internal boundary layer of sufficient height to affect measurements at the 11-m anemometer and produce vertically-heterogeneous behaviour. We describe the turbulence structure of the boundary layer, particularly the corresponding longitudinal integral scale of turbulence for different surfaces, while considering the effect of the internal boundary layer for the development of onshore flow. A methodology is developed to ensure independence from the internal boundary layer for onshore flow. The effect of stability on the integral longitudinal scale of turbulence is analyzed, revealing greater values for unstable atmospheric conditions. In stable atmospheric conditions, differences in surface roughness do not affect the turbulence structure for the anemometer studied.
KeywordsCoastal zone Sensible heat flux Integral scale Roughness length Sonic anemometry
The authors are grateful to the National Hydrography Office of the Ministry of Transport of Uruguay for financing the project for which the measurement station was established. In addition, Telefónica S.A. is thanked for allowing the use of its tower at the port of La Paloma, as is the National Army for providing security and allowing site access.
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