A Lake-scale vortex over Lake Superior imaged by SAR and modeled by MM5: a preliminary study

The Lake-Induced Convection Experiment (Lake-ICE) occurred during the 97-98 winter season. For this experiment, a large suite of standard and unusual measurements were made of the Great Lake environment. Among the data sources is synthetic aperture radar (SAR) imagery of the Great Lakes. These images show spatial variations in radar backscatter which can often be related to the instantaneous patterns of wind forcing of the water's surface. Of particular interest for this presentation is a comparison of a SAR image of Lake Superior and MM5 simulation of the weather in and around Lake Superior, both centered on January 14, 1998.

The SAR image shows what can be best described as a spoked, or radiating structure centered on a closed circulation pattern that, taken together, is suggestive of the radar backscatter patterns associated with polar lows or hurricanes.

The simulations were initialized by in situ data,and include additional data input during the 36 hour simulation. The current model setup uses three grids. The largest grid covers the US and has a grid resolution of 81 km. The next grid covers the western Great Lake region and has a resolution of 27 km. The third grid covers Lake Superior and has a resolution of 9 km. Thus far, the simulations predict the presence of a Lake-scale atmospheric disturbance over Lake Superior at the time of the SAR image just described. In particular, the model runs predict what may be described as a lake-scale vortex, a synoptic-feature, or a combination, characterized by a circulation pattern and convergence zones in the approximate location in space and time of comparable features on the SAR image. An initial look at the temporal evolution of the surface wind field seems to indicate that this may be a propagating feature with some intensification from Lake Superior.