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Webinar: What does it really mean for a lake to "turn over"? Radiatively driven convection in a deep lake

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Friday, 20 September 2019, 1:30

Friday, September 20, 2019. 1:30PM. Webinar: What does it really mean for a lake to "turn over"? Radiatively driven convection in a deep lake. Jay Austin, University of Minnesota, Duluth. Sponsored by NOAA’s Great Lakes Environmental Research Laboratory and the Cooperative Institute for Great Lakes Research. More information here

 

Due to the existence of the temperature of maximum density for freshwater (3.98C), springtime heating of a freshwater lake from incident sunlight can result in a process called radiatively-driven convection, where heating at the surface of the lake makes surface waters denser, resulting in full water-column convection. In a deep lake like Lake Superior, this process can dominate the circulation of the lake for two to three months every year, and controls the vertical redistribution of physical, biological, and geochemical properties in the lake during this period. Characteristic features of the convection cells produced are discerned from a set of observations made in Lake Superior over the last several years, from autonomous underwater gliders, turbulence profilers, and moorings, including a large, two-point mooring that consisted of a two-dimensional array of thermistors 180m on a side. Glider data suggests that warm water produced near the surface convect into the lake in chimney-like structures with lateral scales on the order of 10m, and the cells themselves have lateral scales on the order of 100m. Observed vertical velocities on the order of 1cm/s. Temperature anomalies on the order of 0.1K build up during the day, and the water column tends to fully homogenize each night. Developing a better understanding of the dynamics of this convective process is essential to our understanding of the annual development of deep, dimictic lakes.

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