Factors controlling the latent and sensible heat fluxes over Erhai Lake under different atmospheric surface layer stability conditions

The stratification of atmospheric surface layer (ASL) plays an important role in regulating the water vapour and heat exchange across lake-air interface. Based on one-year data measured by Eddy Covariance (EC) technique over Erhai Lake in 2015, the ASL stability (ζ) was divided into six ranges, including unstable, weakly unstable, near-neutral(unstable side), near-neutral(stable side), weakly stable, and stable range. The characteristic of ASL stability conditions and factors controlling the latent (LE) and sensible (H) heat fluxes under different stability conditions were analyzed in this study. The stability conditions of Erhai Lake have noticeably seasonal and diurnal variation, which the near-neutral and (weakly)stable stratification usually occurred before July with frequency of 51.7% and 23.3%, respectively, but most of the (weakly)unstable stratification was observed since July with frequency of 59.8%. Large evaporation occurred even in stable atmospheric conditions, due to the coupled effects of relative larger lake-air vapor pressure difference and wind speed. The relative controls of LE and H by different atmospheric variables are largely dependent on the stability conditions. In stable and unstable range, LE is closely correlated with vapour pressure difference, whereas in weakly unstable to weakly stable range, LE is primarily controlled by wind speed. H is related to wind speed and lake-air temperature difference under stable conditions, but shows no obvious relationship under unstable conditions.