Thermal Signatures of Evaporating Soil Surfaces – on Energy Partitioning and Fluxes into Turbulent Flows.

The partitioning of incoming radiative energy over drying soil surfaces affects surface temperature dynamics (a key input for remote estimation of fluxes to the atmosphere). In the first part, we present a novel physically-based model for coupling evaporative fluxes and surface temperatures yielding analytical expressions for surface temperature and energy partitioning. Model predictions for evaporative flux and thermal fields were in good agreement with infrared thermography (IRT) measurements of drying sand surfaces in the laboratory. The model accurately predicts the evolution of surface energy partitioning and concurrent changes in the Bowen ratio and Priestley-Taylor?s à parameter for a wide range of surfaces and climatic conditions. In the second part of the presentation we focus on thermal signatures of evaporating surfaces (stage-I evaporation) that interact with turbulent air flows. We link theoretically-predicted and experimentally-measured highly-resolved thermal signatures with eddy-induced localized evaporation rates. The IRT measurements enable characterization of both, the turbulent momentum field and surface evaporative fluxes into turbulent air flows. Surface thermal inertia presents a challenge to rapid IRT implementation; we discuss strategies for circumventing these constraints and using the information to assess surface water content including extension to field applications using (rapid) single IR observations.