Using Temperature Fluctuation Measurements to Estimate Meteorological Inputs for Modelling Dispersion During Convective Conditions in Urban Areas

We examine the performance of several methods to estimate meteorological 1 inputs for modelling dispersion in urban areas during convective conditions. Sensible heat 2 flux, surface friction velocity and turbulent velocities are estimated from measurements of 3 mean wind speed and the standard deviation of temperature fluctuations at a single level on a 4 tower at two suburban sites and at one urban site in Riverside, California. These estimates are 5 compared with observations made at these sites during a field study conducted in 2007. The 6 sensible heat flux is overestimated in the urban area, while it is underestimated at a suburban 7 site when temperature fluctuations are used in the free convection formulation to estimate 8 heat flux. The bias in heat flux estimates can be reduced through a correction that depends on 9 stability. It turns out that the bias in heat flux estimates has a minor effect on the prediction 10 of surface friction velocity and turbulent velocities. Estimates of sensible heat flux, surface 11 friction velocity and turbulent velocities are sensitive to estimates of aerodynamic rough12 ness length, and we suggest estimating the aerodynamic roughness length through detailed 13 micrometeorological measurements made during a limited field study. An examination of the 14 impact of the uncertainty in estimating surfacemicrometeorology on concentrations indicates 15 that, at small distances from a surface release, ground-level concentrations computed using 16 estimates of heat flux and surface friction compare well with the those based on observed 17 values: the bias is small and the 95% confidence interval of the ratio of the two concentrations 18 is 1.7. However, at distances much larger than the Obukhov length, this confidence interval 19 is close to 2.3 because errors in both friction velocity and heat flux affect plume spread. 20 Finally, we show that using measurements of temperature fluctuations in estimating heat flux 21 is an improvement on that based on the surface energy balance, even when net radiation 22 measurements are available. 23