# Gradient transport theory

From AMS Glossary

## gradient transport theory

A first-order turbulence closure approximation that assumes that turbulent fluxes of any variable flow down the local gradient of that mean variable; analogous to molecular transport.

This local turbulence closure approach assumes that turbulence consists of only small eddies, causing diffusion-like transport. An example is where the vertical kinematic flux of a pollutant is modeled as being equal to an eddy thermal diffusivity

*K*times the vertical gradient of mean concentration . This theory is*also called*K- theory or eddy-viscosity theory.*Compare*higher-order closure, nonlocal closure, transilient turbulence theory.