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

Abstract

The stratification of the atmospheric surface layer (ASL) plays an important role in regulating the water vapor and heat exchange across the lake–air interface. Based on one year of data measured by the eddy covariance technique over Erhai Lake in 2015, the ASL stability ((Formula presented.)) was divided into six ranges, including unstable ((Formula presented.)), weakly unstable ((Formula presented.)), near-neutral1 ((Formula presented.)), near-neutral2 ((Formula presented.)), weakly stable ((Formula presented.)), and stable ((Formula presented.)). The characteristics of ASL stability conditions and factors controlling the latent ((Formula presented.)) and sensible heat ((Formula presented.)) fluxes under different stability conditions were analyzed in this study. The stability conditions of Erhai Lake have noticeably seasonal and diurnal variation, with the near-neutral and (weakly) stable stratification usually occurring before July, with frequencies of 51.7% and 23.3%, respectively, but most of the (weakly) unstable stratification was observed after July, with a frequency of 59.8%. Large evaporation occurred even in stable atmospheric conditions, due to the coupled effects of the relatively larger lake–air vapor pressure difference and wind speed. The relative controls of (Formula presented.) and (Formula presented.) by different atmospheric variables are largely dependent on the stability conditions. In stable and unstable ranges, (Formula presented.) is closely correlated with the vapor pressure difference, whereas in weakly unstable to weakly stable ranges, it is primarily controlled by wind speed. (Formula presented.) is related to wind speed and the lake–air temperature difference under stable conditions, but shows no obvious relationship under unstable conditions.