Surface temperature fronts in the Great Lakes

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The distribution and variability of surface temperature fronts in the Great Lakes is studied using an 11 year time series (1985 to 1995) of Advanced Very High Resolution Radiometer (AVHRR) images. After the removal of cloud contaminated pixels as well as those potentially ice covered, an edge detection algorithm identifies surface temperature fronts in each image. The probability of detecting a front in the Great Lakes is highly variable from lake to lake as well as seasonally. Fronts during the winter months generally have cold water on their shallow side and appear in progressively deeper water as winter progresses. The properties of the winter fronts are consistent with a formation mechanism involving strong surface cooling over a sloping bottom. A spring transition occurs, whereby these fronts disappear and are replaced by nearshore thermal bar fronts with warm water found on their shallow side. The time of this transition depends upon the lake, occurring first in Lake Erie, next in Lakes Ontario, Huron, and Michigan, and finally in Lake Superior. These fronts are also observed to progress slowly into deeper water as nearshore waters warm. The classical thermal bar front (4°C) is seen in all of the lakes but most of the fronts during the spring peak in frontal activity have temperatures greater than 4°C, suggesting that the thermal bar marks the offshore edge of a more extensive frontal zone. Frontal activity declines during summer in all lakes except Superior.

Publication Title, e.g., Journal

Journal of Great Lakes Research