The Influence of Lake Surface Temperature on Atmospheric Circulations in the Great Lakes Region.

Abstract

Recently, media coverage of extreme weather events has come with the question “Was this storm caused by climate change?” The scientific community has started to develop statistical measures to try to answer this question, but these studies do not gain insight into the physical causes leading to the storm. This thesis will directly look at some of the physical processes within weather systems in the Laurentian Great Lakes region that could be altered in a future climate through a series of convective allowing simulations using the Weather Research and Forecasting Model (WRF). In the Laurentian Great Lakes region, located at the border of Canada and the United States, the existence of the lakes and the lake surface temperature play a key role in the weather and climate of the region. While it is projected that lake temperatures will increase in a future climate, it is still relatively unknown what this change could mean to atmospheric circulations in the region. The case studies presented look at the direct role the lake surface temperature has on these circulations during the cold and warm seasons to understand the sensitivity of these circulations to future climate conditions. For a lake-effect snowfall simulation, it is shown that the lake temperature influences the extent and intensity of the snowfall downwind of the lake, while interactions with the topography downwind of the lakes still have a critical role. Warm season simulations showed little influence from the lake temperature on precipitation amounts. However, various degrees of change were seen in atmospheric circulations, from little to no change in the convective initiation along Lake Michigan due to the passing of a potential vorticity feature, to larger changes over Lake Superior to the structure of the barrier jet and a mesoscale convective system. Collectively, these simulations show the importance of resolving the lakes in climate simulations and feedbacks that may not be resolved at lower horizontal resolutions, especially in winter. These simulations also give a baseline for future work testing the sensitivity of storm systems over the region to other components.