Research article 06 Dec 2018
Research article | 06 Dec 2018
Abstract. To improve the parametrizations of turbulence dissipation rate (ε) in numerical weather prediction models, the temporal and spatial variability of ε must be assessed. In this study, we explore influences on the variability of ε at various scales in the Columbia River Gorge during the WFIP2 field experiment between 2015 and 2017. We calculate ε from five sonic anemometers all deployed in a ~ 4 km2 area; and from two scanning Doppler lidars and four profiling Doppler lidars, whose locations span a ~ 300 km wide region. We retrieve ε from the sonic anemometers using the second-order structure function method, from the scanning lidars with the azimuth structure function approach, and from the profiling lidars with a novel technique using the variance of the line-of-sight velocity. Turbulence dissipation rate shows large spatial variability, even at the microscale, especially during nighttime stable conditions. Orographic features have a strong impact on the variability of ε, with the correlation between ε at different stations being highly influenced by terrain. ε shows larger values in sites located downwind of complex orographic structures or in wind farm wakes. A clear diurnal cycle in ε is found, with daytime convective conditions determining values over an order of magnitude higher than nighttime stable conditions. ε also shows a distinct seasonal cycle, with differences greater than an order of magnitude between average ε values in summer and winter.
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