Tuesday, 13 January 2009: 2:15 PM
An observational study of the movement of Lake Breeze Fronts in the vicinity of Chicago, IL
Room 124A (Phoenix Convention Center)
Due to high population concentration, the evolution of lake-breezes in near-shore urban areas can have a large impact on society, especially when dealing with heat wave relief and dispersion of pollutants. If heat waves become more frequent and severe, as expected in the Great Lakes region, precise forecasts of the movement of lake-breeze fronts will be crucial for effective management of utilities in urban areas. Previous studies have produced conflicting results on the impacts of urban areas on local sea- and lake-breeze movement. To date, no long-term observations of sea- or lake-breeze movement in urban and nearby areas are available to evaluate these past results. In order to better understand the interaction between lake-breezes and urban landscapes, forty-nine lake-breeze cases in spring and summer 2005 were identified through analysis of WSR-88D radar, surface data and visible satellite images of the Chicago, IL area. Radar data were analyzed to identify the position of the lake-breeze front for every 5 to 10 min during each of the cases. This allowed for a thorough analysis of the temporal and spatial evolution of the lake-breeze front in the vicinity of Chicago, IL.
The peak frequency of lake-breezes occurred in August, during which 12 cases were identified. A less defined peak occurred in June, with 8 lake-breeze cases. Many of the cases involved substantial inland propagation of the lake-breeze front, with nearly one third propagating beyond the KLOT radar site located approximately 50 km from Lake Michigan. While recent numerical modeling studies have suggested that the motion of the lake-breeze front should be slower once they reach the center of the urban heat island circulation, less than one quarter of the 49 lake-breeze fronts had slower motion near Chicago. Interestingly, two thirds of the lake-breeze fronts did not resemble the general shape of the coastline of southwest Lake Michigan, as observed in several recent studies. This research seeks to determine the relative importance of non-uniform surface friction, urban heat island thermodynamic properties, the shape of Lake Michigan's coastline, and environmental and lake-surface conditions on variations in lake-breeze movement in the region. Potential applications of GIS in examining variations in the evolution of lake-breeze fronts will also be discussed.