Extended Abstract (132K)10.2
Comparison of scalar roughness lengths measured at an urban site and two rural sites
Gabriel G. Rooney, Met Office, Bedford, United Kingdom; and B. M. Claxton
The proposed contribution presents and discusses calculations of temperature and momentum roughness lengths z0T and z0q made from measurements above an urban site, and compares them with values obtained by the same method above a flat rural site, and from different measurements above a hilly rural site.
The urban measurements were taken in Birmingham UK during all of July 2000, and consist of hourly statistics of mean wind, temperature and moisture, and momentum, temperature and moisture fluxes measured at 45m, as well as screen, surface and infrared surface temperature measurements and screen humidity measurements. The same quantities measured at the Met Office Field Site (Cardington) have been used for the comparison over flat rural terrain, and balloon-borne and surface measurements over Welsh hills are used for the hilly rural comparison.
The method for calculating the scalar roughness lengths consists of screening the data (of mean values at height, fluxes at height, and mean surface values) for those within the stability limits of Monin-Obukhov flux scaling. The roughness lengths are then obtained as being those which provide the optimal fit between theory and the screened data. It is shown that different values of roughness length may be obtained depending upon which measurement is chosen as representative of the surface mean value, in line with the 'resistance' model of surface fluxes.
The comparison between the sites reveals that, between the urban and flat rural sites the urban scalar roughness lengths are smaller by one to three orders of magnitude. The analysis of the hilly rural site is ongoing, but this comparison is intended to show what differences in parameterisation these two types of complex terrain require for the modelling of scalar fluxes.
Session 10, Roughness lengths, surface resistances and CO2 Fluxes
Wednesday, 22 May 2002, 1:30 PM-3:15 PM
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