An Indirect Estimation of Convective Boundary Layer Structure for Use in Pollution Dispersion Models

Abstract

Dispersion models of the convectively driven atmospheric boundary layer (ABL) often require as input meteorological parameters that are not routinely measured. These parameters usually include the surface fluxes of heat and momentum ?Cpw???and ?u?w?, the height of the capping inversion Zi, the mean wind speed ?(z), wind direction AZ(z) and potential temperature profiles ?macr;(z) up to Zi, and the profiles of the turbulent wind components σu(z), σv(z), and σw(z). Through use of a simple inversion rise model, surface layer flux-profile relationships, and similarity scaling laws for the convective ABL, we demonstrate the accuracy with which the required meteorological parameters can be deduced using much simpler and more readily available measurements. These measurements consist of an early morning temperature profile obtained from a radiosonde ascent; surface layer values of ?, AZ, σu and σv at a single level; either two levels of mean temperature near the surface, or alternatively the incoming solar radiation; and an estimate of the local surface roughness. Predicted values of each of the required parameters are compared with directly measured values, as a function of height or of time, for 26 days of data. Except for AZ(z), each of these parameters can be estimated with a mean bias of less than 15% and a standard deviation ranging from 10 to 40%. In contrast, simple AZ parameterizations often fail to predict the observed wind direction profile accurately; it is suggested that this is due to large-scale terrain inhomogeneities. The role of averaging time in estimating the error of an individual realization is discussed.