The air-water heat exchange and water vertical stability in the Xiangxi Bay of Three Gorges Reservoir

Abstract

水库或湖泊的热分层结构是其动力与环境过程的重要研究方面,虽然很多学者针对水体分层结构和演变机理开展了大量研究,但水体通过水-气界面与大气进行热交换的过程,各气象因子的贡献机理等研究成果还很缺乏。本文基于三峡水库香溪河库湾2019年3月-2020年2月期间的水温、水位及气象等监测数据,针对水-气界面热交换过程如何影响水温垂向结构及表层水体湍流混合作用开展研究。结果表明,(1) 香溪河水体年内呈高温期分层、低温期混合的基本特征,高温期混合层深度小于8 m,低温期混合层深度超过30 m。(2) 太阳短波辐射是香溪河水体的主要热源,潜热通量和长波辐射是香溪河水体的主要冷源,感热通量贡献极小。(3) 香溪河平均风速较弱,约为1.6 m/s,主要通过增强潜热和感热通量的方式影响水体垂向稳定性结构特征,其机械扰动作用较弱。(4) 表层水体湍能通量在高温期较低(10^-7 m³/s³量级),此时水体处于分层状态,风应力大概率主导表层水体湍流发育; 低温期表层水体湍能通量较高(10^-6 m³/s³量级),此时潜热通量和长波辐射主导表层水体湍流发育。;The thermal stratification structure of a reservoir or a lake is important to its dynamics and environmental process. Although many scholars have studied this topic, a gap is still existed on the process of heat exchange in the air-water interface and the contribution mechanism of various meteorological factors. In this paper, based on the observation data of water temperature and meteorology from March 2019 to February 2020, in Xiangxi Bay of the Three Gorges Reservoir, we studied how the heat flux and wind stress affect the vertical structure of water temperature and the turbulent mixing. We have conclusions as following. (1) The Xiangxi River is characterized as stratification in high temperature period and mixing in low temperature period. The depth of mixing layers in high temperature period is less than 8 m and that in low temperature period is more than 30 m. (2) Solar short-wave radiation is the main heat source of Xiangxi Bay, while latent heat flux and long wave radiation are the main cold source. The contribution of sensible heat flux is quite small. (3) The wind speed in Xiangxi River region is weak, with an average value about 1.6 m/s, which influence the water vertical stability by enhancing latent heat and sensible heat flux strongly and mechanical disturbance effect weakly. (4) The turbulent energy flux of surface water is much lower in the high-temperature period (10^-7 m³/s³ in magnitude), at which time the wind stress dominates the development of turbulence. The turbulent energy flux is quite high during low-temperature period (10^-6 m³/s³ in magnitude), when the sensible heat flux and long wave radiation dominate the turbulence mixing.