Observations of boundary-layer winds in an urban environment

During July 2003 the Joint Urban 2003 field campaign was conducted in and around downtown Oklahoma City, Oklahoma. As part of this effort, a network of sodars and minisodars were deployed along a north-south transect through the center of city. The sodars and minisodars were operated for nearly all daylight hours during the campaign. Data from these instruments provide the opportunity to examine the change of wind speed and direction as a function of height as a column of air moves through the city.

Preliminary work has focused on measurements made using two sodars, one approximately 2 km upwind and one approximately 1 km downwind of the downtown core. Our findings are consistent with the expected response of boundary-layer winds to a change in surface roughness. Wind speed measured near the surface is larger upwind of the downtown core. There is greater variability in the wind direction measured downwind of downtown, and there are instances during which the wind direction measured at the downwind site is opposite to the wind direction measured upwind. There are occasions during which there systematic differences in the wind direction over periods of an hour or more. At an altitude 150 m above ground level, the wind speed and wind direction measured by the two sodars are virtually indistinguishable.