大气湍流非平衡态的垂直速度–热通量耦合效应：观测验证与模型优化

Vertical Velocity-Heat Flux Coupling Effects in Nonequilibrium Atmospheric Turbulence: Observational Validation and Model Optimization

摘要: 大气湍流的垂直速度与水热通量(感热与潜热)之间存在交叉耦合效应，借助非平衡态热力学理论和Onsager倒易关系可以推导其耦合系数的函数形式，但受不同观测条件影响缺乏普适性。本文使用黑河流域盈科绿洲均质农田下垫面的气象及通量观测数据，验证和拓展该交叉耦合系数函数的适用性。在垂直速度–水热通量耦合效应的物理机制基础上，引入粒子群优化算法提高耦合系数的拟合精度，建立更合理的经验函数方程；并以潜热通量为例，通过上升/下沉气流条件下潜热通量的估算与观测对比，评估耦合修正前后的模型精度差异。发现采用新拟合的耦合系数后，潜热通量在不同垂直运动条件下的估算值与观测值之间的系统偏差由21%减小至10%，这反映了垂直速度耦合效应在水热(尤其是潜热)通量输送过程中的重要性，表明考虑耦合项能够明显改善对该均质农田下垫面实际湍流通量的估算性能。基于该站点实测资料验证和优化的交叉耦合系数模型，适用于表征此类下垫面大气湍流中可观测且可量化的垂直速度耦合机制。这为深入理解湍流输送特征及改进经典湍流参数化方案提供了参考，也为在高原或非均匀下垫面等复杂环境下开展湍流耦合效应研究提供了初步的科学参考和方法借鉴。

Abstract: There is a cross-coupling effect between the vertical velocity and water-heat fluxes (sensible and latent heat) of atmospheric turbulence. The functional form of the coupling coefficients can be deduced with the help of the nonequilibrium thermodynamic theory and the Onsager reciprocity relation, but it lacks universality depending on the different observation conditions. The applicability of the cross-coupling coefficient function is verified and extended in this paper by using the meteorological and flux observation data from homogeneous farmland surfaces in the Yingke Oasis Station of the Heihe River Basin. Based on the physical mechanism of velocity-water-heat flux coupling effect, a particle swarm optimization algorithm is introduced to improve the fitting accuracy of the coupling coefficients, and a more reasonable empirical functional equation is established; using latent heat flux as an example, the difference in model accuracy before and after the coupling modification is assessed by comparing the estimation of latent heat fluxes under the updraft/sinking airflow conditions with observations. It is found that the systematic deviation between the estimated and observed heat fluxes under different vertical motion conditions is reduced from 21 % to 10 % with the newly fitted coupling coefficients, which reflects the importance of the vertical velocity coupling effect in the transport of water-heat fluxes (particularly latent heat), and suggests that the consideration of the coupling term can significantly improve the estimation performance of the actual turbulent fluxes over this homogeneous farmland surface. The validated and optimized cross-coupling coefficient model based on measured data from this site is suitable for characterizing the observable and quantifiable vertical velocity coupling mechanism in atmospheric turbulence over such surfaces. This provides a reference for a deeper understanding of the turbulent transport characteristics and improvement of the classical turbulence parameterization scheme, as well as preliminary scientific guidance and methodological insights for the study of turbulence coupling effects in complex environments such as plateaus or non-uniform subsurface.