September 8, 2017 - 2:00 pm
September 8, 2017 - 3:00 pm
Address120 David L Boren Blvd, Room 5600, Norman, OK 73072 View map
Scale dependence of Monin–Obukhov similarity theory — Sampling convergence and surface-layer closure
Monin–Obukhov Similarity Theory (MOST) is the ubiquitous frame- work for the estimation of interfacial fluxes at the bottom of atmo- spheric models: they are commonly estimated using flux–gradient clo- sures derived from MOST. Motivated by tower-measurements, MOST is conceptually designed for averaged flow-samples and does not take into account non-local and variation effects. Hence, the rarely encoun- tered limit of an infinite homogeneous surface is an assumption un- derlying MOST. Despite known conceptual and practical deficiencies over heterogeneous surfaces, MOST or versions thereof, such as the MOSAIC approach, are routinely applied over heterogeneous surfaces. I will present a systematic assessment of temporal and spatial validity limits of MOST by use of direct numerical simulation of Ekman flow, a simplified representation of the atmospheric boundary layer. This analysis provides the scale limits of MOST in both time and space on a physical basis, based on first principles only. Further, I unveil a se- vere underestimation of the variability of the actual surface quantities when expressed through MOST as a function of the mean wind at a fixed height within the turbulent boundary layer.