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

Lake- and sea-breezes have been extensively studied using observational, theoretical, numerical modeling, and laboratory techniques. Large population centers in coastal regions make predictability and understanding of these circulations particularly important due to their impacts on dispersion of pollutants, heat wave relief, and energy use. Our group is involved in an investigation of spatio-temporal variability of lake-breezes in the vicinity of Chicago and surrounding suburban areas. This presentation will describe the results of investigations of lake-breeze frontal motions observed by the WSR-88D KLOT radar during 2005.

Radar observations of lake-breeze frontal movement in this region, as identified by radar “fine lines” have revealed some surprising results. A great deal of temporal (day-to-day, intraday) and spatial (urban versus suburban) variability of inland motion of the lake-breeze front was observed, suggesting that lake-breeze/surface/urban heat island interactions may be more complex in urban areas than suggested by several recent studies. In particular, preliminary investigations indicate that lake-breeze movement inhibition in urban heat island centers was observed less than 50% of the time, in contrast to recent findings reported in the scientific literature.

This, in combination with examples of lake-breeze frontal acceleration after passage through the urban center suggests that there may be important differences in how various vertical layers of the lake-breeze interact with the complex surface in this region. For example, both surface friction and urban heat island inhibition of the inland movement of the lake-breeze front would be maximized in the lowest layers. This, in turn, may result in varying responses of the lake-breeze to the urban center. A detailed comparison between radar fine-line position and surface observations will be presented to examine this possibility. Surface, satellite, and ACARS soundings in the region are examined for cases of non-uniform lake-breeze movement in the Chicago region to better understand temporal changes in the movement and vertical structure of the lake-breeze.