Assessing the validity of Monin-Obukhov Similarity Theory over mountainous desert terrain

The validity of Monin-Obukhov Similarity Theory (MOST) over a range of conditions is investigated. The results are based on data collected during the MATERHORN-X field campaign. MATERHORN is a multi-institution, multi-disciplinary project designed to improve weather predictability in mountainous terrain. To this end, a field campaign was conducted at the Dugway Proving Ground in Utah's West Desert, USA from 25 September - 21 October 2012 and from 1 May - 30 May 2013. Here, we present results from three flux towers situated over broadly different surface types to evaluate several aspects of MOST. Two of the sites were over flat terrain and one was situated on a slope (5-7°). The flat sites can be characterized as desert steppe (sparse vegetation ~ 1m tall) and Playa (smooth surface and little vegetation). All towers measured momentum and sensible heat fluxes using sonic anemometers at multiple heights (5 or 6 levels up to 28 m a.g.l.) and employed fast response open path gas analyzers for water vapor and CO2 measurements. We begin our analysis by investigating the constant flux assumption necessary for MOST, which states that the turbulent fluxes in the surface layer should vary by no more than ten percent with height. We are interested in evaluating this assumption over sloping terrain as well as during transitional periods (i.e., when the atmosphere experiences large stability changes in the morning and evening). We evaluate existing universal functions of momentum (φm), sensible heat (φh) , moisture (φq) , and CO2 (φCO2) as well as investigate the scaling relationship of the normalized standard deviations of wind, temperature, moisture, and CO2. We are particularly interested in the formulation of φh during transitional stability. Because the φ functions and the stability parameter contain common divisors, the scaling relationships may be overestimated due to self-correlation. We quantify this error. Finally, we address the non-stationarity of turbulence which can occur under very stable conditions and strongly affect turbulent parameterizations.