Surface current observations by HF radar during EEGLE 2000

HF radar has become an important tool for mapping surface currents in the coastal ocean. However, its use over fresh water has been limited due to much higher propagation loss and smaller wave heights on fresh water lakes. During the Episodic Events Great Lakes Experiment (EEGLE) two multifrequency coastal radars (MCRs), operating between 4.8 MHz and 21.8 MHz, were installed on the southeast shore of the lake, together with an air-sea measurement buoy. Data from the February-April 2000 observations demonstrate HF radar performance characteristics over fresh water as well as characteristics of the surface flow in the lake during periods of moderate to high winds and waves. In early April an episodic event occurred in which strong northerly winds blew down Lake Michigan driving currents down the western shore of the lake past Racine, Wisconsin and Chicago, Illinois and around the southern lake shore to the southeastern shore of the lake. Sediments are resuspended during such an event, putting a variety of pollutants in the water column. These suspended sediments are clearly shown in visible light images from the NOAA-14 satellite. HF radar and buoy measurements of an episodic resuspension event are presented. They show a southward surface current flow at the beginning of the event and then a reversal of the near-shore current as the event progresses and the aforementioned currents move around the bottom of Lake Michigan and reach the St. Joseph, Michigan area. These observations show the interplay of large scale currents from the south and local wind driven currents