Evaluation of an Urban Canopy Parameterization in a Mesoscale Model Using VTMX and URBAN 2000 Data

Abstract

A modified urban canopy parameterization (UCP) is developed and evaluated in a three-dimensional mesoscale model to assess the urban impact on surface and lower-atmospheric properties. This parameterization accounts for the effects of building drag, turbulent production, radiation balance, anthropogenic heating, and building rooftop heating/cooling. U.S. Geological Survey (USGS) land-use data are also utilized to derive urban infrastructure and urban surface properties needed for driving the UCP. An intensive observational period with clear sky, strong ambient wind, and drainage flow, and the absence of a land–lake breeze over the Salt Lake Valley, occurring on 25–26 October 2000, is selected for this study. A series of sensitivity experiments are performed to gain understanding of the urban impact in the mesoscale model. Results indicate that within the selected urban environment, urban surface characteristics and anthropogenic heating play little role in the formation of the modeled nocturnal urban boundary layer. The rooftop effect appears to be the main contributor to this urban boundary layer. Sensitivity experiments also show that for this weak urban heat island case, the model horizontal grid resolution is important in simulating the elevated inversion layer. The root-mean-square errors of the predicted wind and temperature with respect to surface station measurements exhibit substantially larger discrepancies at the urban locations than their rural counterparts. However, the close agreement of modeled tracer concentration with observations fairly justifies the modeled urban impact on the wind-direction shift and wind-drag effects.

NARAC: an emergency response resource for predicting the atmospheric dispersion and assessing the consequences of airborne radionuclides

“…The reader is referred to Nasstrom, et al (2005) for a more complete description NARAC and a comprehensive list of references.…”

“…NARAC routinely runs its own version of the Naval Research Laboratory's (NRL) Coupled Oceanographic and Atmospheric Mesoscale Prediction System (COAMPS) model (Hodur, 1997), which can produce forecasts for any region on Earth. NARAC has developed an urban canopy parameterization for COAMPS (Chin et al, 2005), that improves the representation of urban flow fields. Several external agencies provide NARAC with continuous flows of forecast data from NWP models, including the National Weather Service (NWS) GFS model, the U.S. Navy NOGAPS model, the NWS ETA model, and the NWS RUC model.…”

Overview of an Urban Canopy Parameterization in COAMPS

“…The model is a fully, non-hydrostatic model with several options for turbulence parameterization, cloud processes and radiative transfer. We have recently modified the COAMPS code to include building and other urban surfaces effects in the mesoscale model by incorporating an urban canopy parameterization (UCP) (Chin et al, 2005). This UCP is a modification of the original parameterization of (Brown and Williams, 1998), based on Yamada's (1982) forest canopy parameterization and includes modification of the TKE and mean momentum equations, modification of radiative transfer, and an anthropogenic heat source.…”

“…The addition of the rooftop surface energy equation enables the modified UCP to exhibit a more reasonable diurnal cycle of the heat island effect (Chin et al 2000), which produces the nighttime warming with the maximum near-sunrise and daytime cooling as observed in many field experiments (Garstang et al 1975.;Oke, 1982;Bornstein, 1987). This modified UCP also results in stronger nighttime warming/daytime cooling with increasing roof fraction.…”

“…These values have been derived from satellite imagery for Salt Lake City and should be examined and modified accordingly as new data are obtained and more objective techniques are developed. For a complete listing of the USGS land-use categories, see the tables in Chin et al, (2005) Unlike the urban surface properties, the urban infrastructure properties for a given land-use category (e.g., building height and anthropogenic heating) may greatly vary from city to city. Urban infrastructure properties shown in are based on the satellite aerial photo to estimate the urban and roof fraction information for the Salt Lake Valley.…”