川南森林下垫面不同高度TKE收支特征及通量分析

Analysis of TKE Revenue and Expenditure Characteristics and Flux at Different Heights of the Underlying Surface of the Southern Sichuan Forest

摘要: 本文基于川南地区四峨山森林下垫面的微气象资料和涡动相关系统的湍流观测资料，分析了湍流动能(TKE)收支方程，结果表明：1) 剪切项在大气层结不稳定时增加，而在大气层结不稳定时减少，说明不稳定层结促进湍流发展，稳定层结抑制湍流发展。随着高度增加剪切项逐渐减小，这说明风速变大对剪切项增加有正作用。2) 浮力项随着日照强度的变大而逐渐增强，具有明显的日变化特征。不稳定层结有利于浮力项做正贡献，稳定层结多为负贡献，因此在大气层结阴稳定的阴天天气条件下，浮力项明显被抑制，且多表现为负贡献，且随着高度增加，浮力项逐渐减小。3) 湍流动能总值日变化特征明显，半数时间在20 m处湍流能量最强，表现出剪切项的极大值处与湍流动能总量极大值处相对应的规律。晴天大气层结稳定，剪切项占主导；在层结不稳定时，浮力项强烈发展并占主导地位，两项的主导关系几乎与层结情况完全相符，并与具体稳定度有很强的关联性，即层结不稳定性越强，浮力项越占主导，层结稳定性越强，剪切项越占主导；阴天天气由于一天内都是稳定层结且风速较大，浮力项被抑制，剪切项占明显主导地位。两种天气条件下都表示出剪切项贡献随着高度增加，风速增大，变得更能占主导地位。

Abstract: Based on micrometeorological data and turbulence observations from the eddy covariance system under the forest canopy in the Si’e Mountain region of southern Sichuan, this paper analyzes the turbulent kinetic energy (TKE) budget equation. The results indicate that: 1) The shear term increases in unstable atmospheric stratification and decreases in stable atmospheric stratification, suggesting that unstable stratification promotes turbulence development while stable stratification suppresses it. As height increases, the shear term gradually decreases, indicating that an increase in wind speed positively affects the shear term. 2) The buoyancy term strengthens with increasing solar radiation intensity, showing a clear diurnal variation. Unstable stratification contributes positively to the buoyancy term, while stable stratification mostly contributes negatively. Therefore, under stable stratification conditions on cloudy days, the buoyancy term is significantly suppressed and mostly negative, and it decreases with height. 3) The total turbulent kinetic energy (TKE) shows a clear diurnal variation, with the strongest turbulence occurring at 20 meters during half of the observed time, demonstrating a correlation between the maximum shear term and the maximum total TKE. On sunny days, when the atmospheric stratification is stable, the shear term dominates. In unstable stratification, the buoyancy term develops strongly and becomes dominant. The dominant relationship between these two terms aligns closely with the stratification conditions and is strongly associated with specific stability levels. The stronger the instability, the more dominant the buoyancy term; the stronger the stability, the more dominant the shear term. On cloudy days, with stable stratification throughout the day and higher wind speeds, the buoyancy term is suppressed, and the shear term clearly dominates. Under both weather conditions, it is evident that with increasing height and wind speed, the shear term becomes more dominant.