Observations of Near-surface Heat Flux and Temperature Profiles through the Early Evening Transition Over Contrasting Surfaces

Monin-Obukhov Similarity Theory (MOST) is the basis for nearly all flux-gradient relationships within the atmospheric surface layer. It is found to some degree in nearly all numerical weather models and is used extensively to organize and communicate mean and turbulent flow statistics. Two of the most limiting assumptions behind its derivation are that the surface is flat, homogeneous and that the flow is quasi-stationary. Sloping, rough terrain and morning and evening transitional periods are notable violations of these assumptions. Here, data are used from the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program to examine the applicability of MOST over rough, sloping surfaces as well as during transitional periods in the morning and evening. MATERHORN is a multi-institution, multi-disciplinary project designed to improve weather predictability in mountainous terrain. Two field campaigns were conducted at Dugway Proving Ground in Utah's West Desert, USA, from 25 September – 21 October 2012 and from 1 May – 30 May 2013. We present results from two flux towers situated over broadly different surface types. The first site is characterized as desert steppe with sparse vegetation (~ 1m tall), the second site as playa (dry lake bed with smooth surface and no vegetation). At both sites, momentum and sensible heat fluxes were measured at multiple heights (5 or 6 levels up to 28 m agl) using sonic anemometers and fine wire thermocouples, and arrays of 20-25 thermocouples measured temperatures between 1 cm and 3.2 m agl. We find that MOST performs adequately for the flat sites under moderate stabilities. The universal functions,