Real time observation of the thermal bar and spring stratification of Lake Michigan with the GLUCOS coastal observatory

During the spring of 2008 a subset of the WATER Institute´s Great Lakes Urban Coastal Observing System (GLUCOS) was deployed to demonstrate the ability of the observatory to remotely monitor, in real time, the seasonal transition from a mixed state to a stratified state in coastal Lake Michigan. A prominent feature of this transition is the spring thermal front, also known as the thermal bar, a boundary of 4degC water that extends from top to bottom and separates near-shore stratified water from colder, mixed water further off-shore. Three Pioneer II buoys were deployed in a west to east line at 20 m, 40 m and 60 m depths and at distances of 2 km, 6 km and 12 km from shore respectively. Each buoy was equipped with a string of temperature sensors spaced one meter apart from the bottom to about 3 meters below the surface. The buoys communicated with a shore station using 900 MHz radio modems. An Internet connection was established between the WATER Institute and the buoys via the shore station permitting two-way communication for real-time data retrieval and control of the buoys. The spring thermal transition was remotely observed at the 20 m buoy along with its characteristic 4degC thermal bar. This paper will present the data on the spring thermal evolution of the lake as measured by the GLUCOS observatory and will describe the design of the new Pioneer II buoy that made-up the buoy array for this experiment.