Abstracts for the 6th International GAME Conf.

3-5 December 2004

Kyoto Japan

New models of the unstable atmospheric surface layer

Keith G. McNaughton (1)

For the last 50 years Monin-Obukhov similarity theory has provided the foundation for nearly all models of the atmospheric surface layer. This theory proposes that turbulence processes there layer depend on only three variables: observation height z, friction velocity u*, and the buoyancy parameter gH/T. This model was developed when turbulence was still thought to consist of small bodies of fluid (eddies) with short lifetimes and erratic movements, carried along by the mean flow. Such eddies respond only to local conditions in the flow, so larger-scale influences were not considered. Recently two new models have been developed which assign much greater importance to the turbulence in the outer layer. The new models of Hunt and Morrison (Euro. J. Mech. B - Fluids 19, 673-694, 2000) and McNaughton (Bound.-Layer Meteor. 112, 199-221, 2004) both see turbulence in the atmospheric surface layer as being the direct product of eddies from the outer convective layer interacting with the ground. Hunt and Morrison propose that eddies moving down from the outer layer encounter strong shear near-surface, causing them to be rapidly distorted. They use the linearizing assumptions of rapid distortion theory to develop a model of this process. By contrast, McNaughton sees the larger eddies from the outer layer as creating the shear near the ground, which shear has both mean and variable components. This shear powers the upscale development of coherent structures that initiate continuously at the ground and develop upwards as cascades. This model is intrinsically non-linear. It describes a self-organizing complex dynamical system of eddies with a strange attractor whose scale velocity, but not form, depends on the local instability. The paper will point out some testable predictions of the new models.

Submittal Information

Name : Date :
    Dr Keith G. McNaughton
    16-Sep-04-00:51:03
Organization : Theme :
    School of GeoSciences, The University of Edinburgh
    Theme 1
Address : Presentation :
    Kings Buildings, Mayfield Road, Edinburgh EH9 3JU, Scotland
    Poster or oral
Country : Abstract ID :
    United Kingdom
    T1DKGM16Sep04005103
Phone : Fax :
    +44 131 650 7728
    +44 131 662 0478
E-mail :
    keith.mcnaughton@ed.ac.uk