Urban-Rural Differences in Tower-Measured Winds, St. Louis

Abstract

Hourly averaged winds from 30 m towers of the RAMS network (St. Louis region) are analyzed to determine systematic differences between urban and rural wind speed and direction. Previous studies of tower winds in London and New York have advanced the notion of a critical wind speed (?4 m s?1) below which speeds are higher in the city than in the adjacent countryside. This apparent acceleration of low-speed flows has been explained as resulting from the dominance of heat island effects over roughness effects. Analyzing observations from all of 1976, this study finds slightly higher speeds in central St. Louis only under nearly calm conditions, typified by a weak heat island and convective instability. This result raises doubts about the universal applicability of the concept of a critical wind speed as previously formulated.