Observations of spatially-variable lake-breeze movement in the vicinity of Chicago, IL

Lake-breezes are known to have an impact on the dispersion of pollutants, heat wave relief, and energy use, particularly in coastal urban areas (e.g., Chicago, IL). While recent numerical model simulations have suggested that sea- or lake-breezes should move more slowly through urban areas than in the surrounding suburbs, there have been few fine-scale observations of the spatial and temporal variations in lake-breeze movement to evaluate these results. Accordingly, lake-breeze cases from spring and summer 2005 were identified using a combination of WSR 88-D KLOT radar, surface and visible satellite observations. The hourly position of the radar fine line was used to determine the speed of the inland movement of the Lake Breeze Front (LBF) along several cross-sections throughout the Chicago, IL area. A great deal of temporal (day-to-day, intraday) and spatial (urban versus suburban) variability of inland motion of the LBF was noted.

Two cases from summer 2005, June 21 and August 28, were analyzed in more detail in an attempt to understand the mechanisms which led to the fine-scale variations in LBF movement observed on those dates. During the June 21 case, initial inland movement of the LBF was slower in downtown Chicago relative to movement in the suburbs. However, after the LBF passed through the city, some segments of the LBF accelerated inland. By the evening of June 21, the LBF progressed more than 130 km inland. Alternatively, on August 28, the LBF moved inland more quickly through downtown Chicago, relative to the suburbs. By the evening of August 28, the LBF had progressed more than 50 km inland. Analyses of ACARS data and surface data from the Illinois EPA will be shown for these cases.