ESTIMATING METEOROLOGICAL INPUTS FOR URBAN DISPERSION MODELS

Meteorological variables such as surface friction velocity and heat flux are critical inputs to the current generation of dispersion models such as AERMOD. This paper examines methods to estimate these variables by applying Monin-Obukhov (M-O) similarity to measurements made on towers located in urban areas. The inputs to these methods are restricted to the wind speed and the standard deviation of temperature fluctuations data measured at a single level on a tower. The performance of these methods are evaluated with data collected at one urban and two suburban towers in Riverside, California during two months in 2007, The data consisted of mean winds and temperatures as well as heat and momentum fluxes using a sonic anemometer at one level on each tower. The major conclusions of this study are that during unstable conditions: 1) M-O theory provides adequate estimates of micrometeorological variables using urban measurements of mean winds and temperatures at one level when the standard deviation of temperature fluctuations is used to estimate heat flux, 2) the simple free convection estimate provides estimates of the heat flux that compare well with those from methods that account for stability effects through the M-O length, 3) all the methods overestimate heat flux close to neutral conditions, 4) the overestimation of heat flux does not appear to affect estimates of surface friction velocity, but results in overestimation of the vertical turbulent velocity. During stable conditions, 1) vertical and horizontal velocity fluctuations are related to friction velocity through similarity relationships derived in flat terrain, 2) estimates of the surface friction velocity based on temperature fluctuations do not improve upon those based on a constant value o