The very stable boundary layer in flat versus complex terrain: CASES-99 versus T-REX

At the Terrain-Induced Rotors Experiment, three 30 m towers were nested within the larger experimental array in order to provide flux profiles representative of the Owens Valley and a mountainous site. The Owens Valley is a flat-bottomed deep (1.5 km) valley at 1 km MSL on the east side of California's Sierra Range. Measurements by sonic anemometer were made at 6 levels starting at 5 m in 5 m intervals on each of the towers, and the towers were placed so that their representativeness could be assessed. Local roughness length was 0.06 m. At CASES-99 a single 60 m tower provided flux profiles over nearly flat (local slopes of ~ 0.5o) terrain, and in this case the flux profiles are assumed to be representative of the local area and a plains site over roughness of 0.01 m.

In this work, the first results of an intercomparison between the very stable boundary layer at these two vastly different sites is made, with an emphasis on the relative magnitude of heat and momentum fluxes and the relevant time and space scales for intermittent turbulence. Flux profiles are also shown which indicate the influence of the complex orography on the mean structure of the mountainous region surface layer relative to that over the plain. Implications for the applicability of surface layer theory application in numerical models of the very stable boundary layer are discussed.