Spatial and temporal variability of turbulence dissipation rate in complex terrain

To improve parameterizations of the turbulence dissipation rate (epsilon) in numerical weather prediction models, the temporal and spatial variability of epsilon must be assessed. In this study, we explore influences on the variability of epsilon at various scales in the Columbia River Gorge during the WFIP2 field experiment between 2015 and 2017. We calculate epsilon from five sonic anemometers all deployed in a similar to 4 km(2) area as well as from two scanning Doppler lidars and four profiling Doppler lidars, whose locations span a similar to 300 km wide region. We retrieve epsilon 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. The 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 epsilon, with the correlation between epsilon at different stations being highly influenced by terrain. epsilon shows larger values in sites located downwind of complex orographic structures or in wind farm wakes. A clear diurnal cycle in epsilon is found, with daytime convective conditions determining values over an order of magnitude higher than nighttime stable conditions. epsilon also shows a distinct seasonal cycle, with differences greater than an order of magnitude between average epsilon values in summer and winter.