SOME BASIC PROPERTIES OF THE SURROGATE SUBGRID-SCALE HEAT-FLUX IN THEATMOSPHERIC BOUNDARY-LAYER

The development of improved subgrid-scale (SGS) models for large-eddy simulation of scalar transport in the atmospheric boundary layer requi res an improved understanding of basic properties of the SGS fluxes. H igh frequency atmospheric wind speed and temperature data sampled at a height of 1.7 m are used to measure SGS heat fluxes and dissipation o f temperature variance, by means of one-dimensional filtering and invo king Taylor's hypothesis. Conditional averaging is used to isolate int eresting features of the SGS signals, and to relate them to the large- scale characteristics of the flow, such as the presence of coherent st ructures. Both mean and conditionally averaged SCS quantities are comp ared with those obtained using a standard eddy-diffusivity model. With in the limitations imposed by the one-dimensional data analysis, we ob serve that the model appears unable to reproduce important features of the real signals, such as the negative dissipation of temperature var iance associated with strong negative resolved temperature gradients d ue to the ejection of warm air under unstable atmospheric stability co nditions.