Partial energy balance closure of eddy covariance evaporation measurements using concurrent lysimeter observations over grassland

Abstract. With respect to the ongoing discussion on the causes of the energy imbalance and approaches to force energy balance closure a method had been proposed which allows the partial latent heat flux closure (Widmoser and Wohlfahrt; 2018). In the present paper, this method is applied to four measurement stations over grassland under humid and semi-arid climate, where lysimeters (LY) and eddy covariance (EC) measurements were taken simultaneously.

Results differ essentially from the ones quoted in literature. We distinguish between resulting EC-values weakly and strongly correlated to LY-observations as well as systematic and random deviations between LY- und EC-values. At the overall average, an excellent match could be achieved between LY and EC-measurements, which were partially closed with evaporation-linked weights. But there remain high differences between standard deviations of LY- and adjusted EC-values. For further studies we recommend data collected at time intervals even below half an hour.

No correlation could be found between correction evaporation weights and weather indices. Only for some datasets a positive correlation between evaporation and the correcting evaporation weight could be found. This effect appears pronounced for cases with high radiation and plant water stress. Without further knowledge on the causes of energy imbalance one might perform full closure using equally distributed weights. Full closure, however, is not dealt with in this paper.