Surface energy-balance closure over rangeland grass using the eddy covariance method and surface renewal analysis

The performance of surface renewal (SR) analysis for estimating sensible heat (H), latent heat (LwE) and carbon dioxide (LpFp) flux, and the closure of the surface energy-balance equation were analyzed in an experiment at a rangeland grass site in the foothills of the Sierra Nevada Mountains (Ione, CA, USA). Both the LwE and H fluxes in late fall, winter, and early spring (the wet period) were relevant in the energy-balance, but from early spring to fall (dry period), most of the available net surface-energy contributed to sensible heat flux. The site is influenced by regional advection and some degree of dissimilarity between temperature and the other two scalars was observed. To our knowledge, this is the first paper evaluating the capability of SR analysis to (1) close the energy-balance on a long-term experiment and (2) estimate carbon dioxide flux. The SR analysis performance was evaluated in terms of the correlation with fluxes from the eddy covariance (EC) method and its capability to close the surface energy-balance. Regardless of the weather conditions, the EC closure underestimated the available energy by about 10%, but the performance was slightly better during dry rather than humid conditions. In contrast, the SR closure was always good and did not favor wetness conditions. Despite the lack of similarity, the energy partitioning provided by SR analysis was reliable for all three scalars. SR analysis provided reliable Bowen ratio estimates. Under stable atmospheric conditions fluxes were too small to evaluate either method.