Principles used when constructing models for velocity spectra are reviewed. Based upon data from the Kansas and Minnesota experiments, simple spectral models are set up for all velocity components in stable air at low heights, and for the vertical spectrum in unstable air through a larger part of the planetary boundary layer. Knowledge of the variation with stability of the (reduced) frequency f, for the spectral maximum is utilized in this modelling. Stable spectra may be normalized so that they adhere to one curve only, irrespective of stability, and unstable w-spectra may also be normalized to fit one curve.The problem of using filtered velocity variances when modelling spectra is discussed. A simplified procedure to provide a first estimate of the filter effect is given.In stable, horizontal velocity spectra, there is often a 'gap' at low frequencies. Using dimensional considerations and the spectral model previously derived, an expression for the gap frequency is found.

The aim of this paper is to describe the use of a general methodologytailored to the evaluation of micro-scale meteorological models appliedto flow and dispersion simulations in urban areas. This methodology,developed within COST 732, has been tested through a large modellingexercise involving many groups across Europe. The major test caseused is the Mock Urban Setting Test (MUST) experiment representingan idealised urban area. It is emphasised that a full model evaluationis problem-dependent and requires several activities including astatistical validation that requires a careful choice of the metricsfor the comparison with measurements

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