## eddy flux

(

*Or*turbulent flux.) The rate of transfer of a conservative fluid property through a surface by turbulent eddies.In the case of an unchanging mean state, the eddy flux of a property where lower case represents turbulence values (fluctuations from the mean), where where θ is the temperature fluctuation, where where

*S*in the*z*direction is expressed by*w*represents vertical velocity, ρ density, and the bar represents the mean over a chosen period. By analogy with molecular diffusion, the eddy flux in the planetary boundary layer is often expressed by*K*_{s}is the turbulent transfer coefficient (also turbulent exchange coefficient, or eddy diffusivity). This can be generalized to include eddy diffusion in the horizontal (*x*,*y*) plane. If*S*is replaced by*c*_{p}*T*, where*c*_{p}represents specific heat at constant pressure and*T*represents temperature, the vertical turbulent heat flux (or eddy heat flux) can be represented by*K*_{h}the eddy thermal diffusion coefficient (or eddy conductivity), and Γ represents the adiabatic lapse rate. Similarly, eddy momentum flux is represented by*U*represents the mean speed in the direction of the mean wind, and*K*_{m}represents the eddy viscosity coefficient (or eddy viscosity). Also, the turbulent transfer of water vapor may be expressed in energy units by*L*represents the latent heat of vaporization,*K*_{e}is the eddy diffusion coefficient, and is the specific humidity.*See also*diffusion, turbulence.Fleagle, R. G., and J. A. Businger 1980. An Introduction to Atmospheric Physics. 2d ed., Academic Press, . 266– 272.