J5.1 "Turbulence" with Very Weak Winds and Stable Stratification

Tuesday, 10 July 2012: 10:45 AM
Essex Center/South (Westin Copley Place)
Larry Mahrt, NorthWest Research Associates, Inc., Corvallis, OR

In the stratified boundary layer with very weak winds, the wind field is driven by wave-like motions, microfronts and numerous more complex submeso motions. The turbulence does not achieve equilibrium with the constantly changing wind field. Traditional scaling and similarity theory does not apply and cannot be simply generalized. Alternative scaling variables and stochastic approaches will be explored. Such approaches must account for persistent nonstationarity, atypical boundary layer wind profiles and the fact that the turbulence cannot be cleanly separated from nonturbulent motions. Boundary layer wind profiles include surface wind maxima, strong directional shear and inflection points. A new analysis philosophy will be outlined. With strong nocturnal radiative cooling and weak winds, even minor surface heterogeneity can exert a strong influence on the surface flow and turbulence. Cold air drainage and cold pools may occur simultaneously on a variety of scales, often intermittently. Local thin boundary layers contribute to a regional boundary layer in a way that is not understood. Numerous observational difficulties are noted and future observational needs are outlined
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