Long-term wind speed variations for three midwestern U.S. cities.

Long-term wind speed variations were investigated for three midwestern cities including Indianapolis, IN; Cincinnati, OH; and Little Rock, AR in the continental United States. These cities were chosen because their topography is relatively flat and unaffected by large mountain ranges or other topographical features, they represent important regional economic centers, and they have all undergone major air quality management efforts over the past 35 yr to attempt to meet the National Ambient Air Quality Standards. The hourly data were obtained from the National Climatic Data Center from 1943 to 2008 for Indianapolis and Little Rock and from 1948 to 2008 for Cincinnati. The analysis included calculating the frequency of calms and wind speeds over five different bins for the respective cities. The results indicate a significant increase in the frequency of calms (statistical significance > 99.999%) and a decrease in the overall frequency of other wind speeds for all three cities. Increasing trend in calms is more predominant during the ozone season (April through October). The results from regression analysis, significance testing, and spatial correlation analysis support the argument that a common "midwestern" large-scale atmospheric forcing is influencing surface wind speed in this area. It was found that for all three cities the Pacific North American (PNA) teleconnection pattern has the highest relative association with the trends in wind speed. The results support large-scale continental effects (like teleconnections) as a hypothesis to be examined more closely along with already established evidence of the influence of the Pacific and Atlantic teleconnection anomalies. Reduced wind speed may have implications on air quality management efforts in the region. Increases in the frequency of calms would affect ozone distribution patterns and may suggest a need to make changes to their ozone mitigation strategy. Weaker winds would ventilate pollutants from these areas less effectively, which could be problematic from a human health point of view, particularly for asthmatics.