Investigation of the impact of surface heterogeneity on the surface energy balance non-closure using long-term observations

Abstract Recent studies highlighted that the modelling of surface fluxes of momentum, sensible and latent heat is the second most important issue in the weather and climate numerical models. Eddy-covariance measurements are used to implement and validate those models, but one systematic error is identified and makes the comparison between models and observations tricky : the Energy Balance Non-Closure (EBNC). A one-year field experiment is performed in Toulouse, south-west of France, to document the variability of the land-atmosphere exchanges around the Météopole permanent site. Three indicators that aim to quantify the surface and fluxes heterogeneity are defined and applied to several domain sizes (footprint scale, 1-km-scale and 10-km-scale analysis). They are cross-analysed with the EBNC to investigate the impact of the surface heterogeneity on the non-closure. The results showed that while no systematic nor strong relationship was found, the footprint-scale analysis and the sensible heat flux studies at a 1-km and 10-km-scale seem to have a tendency to match with the variations of the EBNC. By extending the studied domain from 1 km to 10 km, we incorporate a greater heterogeneity in latent heat flux than in sensible heat flux. The impact of the organisation of the surface was studied through an indicator based on the length scale of the surface patches. The results did not suggest fundamentally different outcomes but they did highlight the differences between the 1-km and the 10-km scales, and between the sensible and latent heat flux analysis.