Scalar flux similarity in the layer near the surface over mountainous terrain

The scaled standard deviations of temperature and humidity are studied in complex terrain. The study area is a steep Alpine valley in Austria, with six measurement sites of different slope, orientation and roughness (i-Box, Inn Valley). Firstly, some assumptions forming the basis of Monin-Obukhov Similarity theory (MOST), i.e. constant turbulence fluxes with height and the degree of self-correlation between the involved turbulence variables, are examined. Since the basic assumptions for the applicability of MOST —horizontally homogeneous and flat conditions— are violated, the analysis is performed based on a local similarity hypothesis. The scaled standard deviations as a function of local stability are compared with previous studies from horizontally homogeneous and flat terrain, horizontally inhomogeneous and flat terrain, weakly inhomogeneous and flat terrain, as well as complex terrain. As a reference for this study, similarity formulas, for unstable and stable conditions are calculated, using weakly inhomogeneous and flat data from the Cabauw experimental site in Netherlands (KNMI), assessed with the same postprocessing method as for the i-Box data. Significant differences from the reference curve and also among the i-Box sites are noted, especially for data derived from the i-Box sites with steep slopes. These differences concern the slope and the magnitude of the best-fit curves, pointing out the site-dependence of any similarity theory.