Turbulent heat flux and temperature gradient alignments in the lower atmosphere

Chad Higgins(1), Marc B. Parlange(1,3) & Charles Meneveau(2,3)

1 Department of Geography and Environmental Engineering 2 Department of Mechanical Engineering 3Center for Environmental and Applied Fluid Mechanics, The Johns Hopkins University, Baltimore MD 21218

ABSTRACT: Parameterizations used in Large Eddy Simulations of the atmospheric boundary layer are based on the assumption that subgrid-scale fluxes are aligned against spatial gradients of transported quantities (down-gradient closures). Based on field experiments, we determine the distribution and most likely relative orientations of the SGS heat flux relative to parameterizations based on the temperature gradient. We show that, under neutral and unstable atmospheric stability, the SGS heat flux most likely lies within a plane that is spanned by the temperature gradient vector and its product with the velocity gradient tensor, i.e. within the geometric span of the so called mixed tensor eddy diffusivity model.

Geophys. Res. Letts., 31, L22105 (2004), full pdf article -- (© AGU, see http://www.agu.org/journals/gl/)