Air-Lake Momentum and Heat Exchange in Very Young Waves Using Energy and Water Budget Closure

Turbulent momentum and heat exchanges at the air-water interface of lakes are complex processes due to diverse characteristics such as climate, fetch limitation, and geometry; however, their parameterizations are necessary for hydro- and thermodynamic modeling. In this study, we performed comprehensive research on turbulent exchanges of a shallow, large but highly fetch limited lake employing 5 months of simultaneous eddy-covariance (EC), wave, energy, and water budget measurements. Based on the Monin-Obukhov similarity theory, wind and wave age-related drag coefficients and roughness lengths were derived for very young wave ages. The new drag functions showed an increased water surface resistance compared to marine conditions. In terms of water vapor roughness length and transfer coefficients, an apparent intra-seasonal variation was observed. Turbulent heat fluxes were evaluated by closing the lake's energy budget using the Bowen ratio method. Furthermore, we aimed to close the energy budget by assuring the water balance closure as well through the evaporation (latent heat flux), resulting in significant deviations from the EC-based results. EC-based heat fluxes and transfer coefficients were found to be underestimated on average by 29% and 33%, respectively. The water balance closure suggested that the energy residual should not be distributed based on the Bowen ratio, and sensible heat fluxes were more underestimated than latent heat fluxes. In the case of Lake Balaton, atmospheric stability plays a minor role; however, our analysis revealed significant effects caused by the surrounding topography and water side stratification.

Automated summary

Turbulent momentum and heat exchanges at the air-water interface of lakes are complex processes, and this study provides valuable insights into these processes.