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 ($\zeta$) was divided into six ranges, including unstable ($-1\le \zeta <-0.1$), weakly unstable ($-0.1\le \zeta <-0.01$), near-neutral1 ($-0.01\le \zeta <0$), near-neutral2 ($0\le \zeta <0.01$), weakly stable ($0.01\le \zeta <0.1$), and stable ($0.1\le \zeta <1$). The characteristics of ASL stability conditions and factors controlling the latent ($\mathrm{L}\mathrm{E}$) and sensible heat ($H$) 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 $\mathrm{L}\mathrm{E}$ and $H$ by different atmospheric variables are largely dependent on the stability conditions. In stable and unstable ranges, $\mathrm{L}\mathrm{E}$ is closely correlated with the vapor pressure difference, whereas in weakly unstable to weakly stable ranges, it is primarily controlled by wind speed. $H$ is related to wind speed and the lake–air temperature difference under stable conditions, but shows no obvious relationship under unstable conditions.

Graphical abstract

摘要

本文利用由涡动相关法观测得到的2015年高原开放淡水湖泊 (洱海) 的湍流通量资料, 分析了湖面近地层大气稳定度特征以及不同稳定度条件下潜热和感热通量的主要控制因子。湖面近地层大气稳定度具有显著的日变化和季节变化特征。不同大气变量对潜热和感热通量的相对影响程度受到大气稳定度的调控。在稳定和不稳定范围内, 潜热通量与湖-气间的水汽压差密切相关, 而在弱不稳定到弱稳定范围内, 潜热通量主要受风速控制。在稳定条件下, 风速和湖-气温差对感热通量具有显著影响, 而在不稳定条件下对感热通量的影响不显著。

KEYWORDS:

• Atmospheric surface layer stability
• eddy covariance
• Erhai Lake
• latent and sensible heat fluxes

关键词:

• 近地层大气稳定度
• 涡动相关法
• 洱海
• 潜热和感热通量

Acknowledgments

We appreciate the staff at the Yunnan Provincial Institute of Meteorology and Dali National Climatic Observatory for their help in the maintenance of the measurement site and instruments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by the National Key Research and Development Program of China (No. 2017YFC1502101) and National Natural Science Foundation of China (Nos. 91537212 and 41775018).