从湍流经典理论到大气湍流非平衡态热力学理论

湍流是日常生活中一种普遍的自然现象,也是经典物理学仍未完全解决的难题。湍流更是大气运动的最基本特征。本文系统地回顾了大气湍流经典理论发展简史,进一步详细介绍了大气湍流非平衡态热力学理论。大气湍流非平衡态热力学理论在熵平衡方程中引入动力过程,进而统一推导出大气湍流输送的Fourier定律、Flick定律和Newton定律,证明了Dufour效应、Soret效应、可逆动力过程与热力不可逆湍流输送过程之间的交叉耦合效应,以及湍流强度定理。这些定律和定理中得到了观测的事实验证,同时它们的唯象系数也由观测资料所确定。湍流强度定理揭示,湍流发展的宏观原因是速度和温度的剪切效应,Reynolds湍流和Rayleigh-Bénard湍流共存于大气湍流中。热力过程和动力过程间耦合效应现象的发现突破了传统湍流输送理论,即Fourier定律、Flick定律和Newton定律的观点——一个宏观量的输送通量等价于这个宏观量的梯度湍流输送通量。热力和动力过程间的耦合原理认为,一个宏观量的输送通量包括这个量的梯度湍流输送通量和速度耦合输送通量两部分。因此,能量和物质的垂直输送通量除了相应物理量梯度造成的湍流输送外,还应包括垂直速度耦合效应,即辐散或辐合运动造成的耦合效应。在一个很宽的尺度范围内,地表面的空间特征是非均匀的。下垫面非均匀性造成的对流运动将引起大气的辐散或辐合运动。这可能是导致地表能量收支不平衡的重要原因之一。垂直速度对垂直湍流输送的交叉耦合效应为非均匀下垫面大气边界层理论的发展,并为克服地表能量收支不平衡问题及非均匀下垫面大气边界层参数化遇到的困难提供了可能的线索。

From the Clasic Theory of Turbulence to the Nonequilibrium Thermodynamic Theory of Atmospheric Turbulence

The turbulence is one of the ubiquitous natural phenomena in everyday experience,and a puzzle that is not yet fully resolved in classical physics.All the more so,it is a basic characteristic of the atmospheric motion.This paper reviews by the numbers the develop history of classic theory of atmospheric turbulence,further more introduces detailedly the nonequilibrium thermodynamic theory of atmospheric turbulence.In the nonequilibrium thermodynamic theory of atmospheric turbulence,the entropy equilibrium equation of atmospheric system with dynamic processes is introduced,and then Fourier′s and Flick′s laws,Newton′s Law deducted by,and both the Dufour and the Soret effects,the cross coupling effect between the dynamic and turbulent transport processes in the atmosphere,and the turbulent intensity theorem are uniformly proved by atmospheric nonequilibrium thermodynamics.These laws and theorem are partially validated by using observed data,further to determine their phenomenological coefficients.The turbulent intensity theorem reveals that the macroscopic cause of the development of fluid turbulence is a result of the shearing effects of velocity together with temperature and proves that both Reynolds turbulence and Rayleigh-Bé nard turbulence coexist in the atmosphere.The discovery of the coupling effect phenomenon between the thermodynamic and dynamic processes breaks through the viewpoint of the theories of traditional turbulent transport,Fourier′s and Flick′s laws,and Newton′s Law,i.e.,the transport flux of one kind of macroscopic quantity is equivalent to the gradient turbulent transport flux of this macroscopic quantity.Moreover,the coupling principle between the thermodynamic and dynamic processes deems that the transport flux of one kind of macroscopic quantity should include the velocity coupling transport in addition to the gradient turbulent transport flux of this macroscopic quantity.Consequently,the vertical transport flux of energy and matter should count in the cross coupling effect of the vertical velocity,i.e.,convergence and divergence motion,in addition to the turbulent transport flux caused by their vertical gradient.The earth′s surface is characterized by spatial heterogeneity over a wide range of scales.The heterogeneity of underlying surface brings on the advection to lead the convergence and divergence motion.It may be an important cause of the imbalance of energy budget of the ground surface.The cross coupling principle of the vertical velocity and vertical turbulent transport may offer a possible clue to the theory of atmospheric boundary layer with heterogeneous underlying surface and to overcome the difficulties encountered in the imbalance problem of ground energy budget and in the parameterization of boundary layer with the heterogeneous underlying surface.