Episodic Events and Cross-Margin Transport in the Great Lakes:
HF Radar Observations on Currents, Winds, and Waves

J. Vesecky

The research project proposed here is an integral of an omnibus master proposal entitled, "The Impact of Episodic Events on Nearshore-Offshore Transport in the Great Lakes" submitted by the NOAA Great Lakes Environmental Research Laboratory, Dr. David Schwab et al., principal investigators. The master proposal seeks to Identify and quantify the physical processes generating cross-margin transport of biologically important material during episodic events in the Great Lakes, develop a combined observational and modeling program to identify, quantify and develop prediction tools for these processes, test the hypothesis that a major mechanism for cross-margin transport in the Great Lakes is a forced, two-gyre vorticity wave responding to episodic wind events, and incorporate results into a computer-based Information and forecasting system. Our objective in this research is to make real time measurements of key air and water variables necessary for the aforementioned observational, modeling and forecasting activities, in particular surface currents, winds and waves that are pertinent to the overall objectives above. Our proposed role is to deploy two multifrequency HF radar units along the shore of lower Lake Michigan (near St. Joseph) to provide (to this research consortium and other users) real time observations of near surface current and current shear, wind direction and wave height over an area of about 2500 sq. km. adjacent to the lower Lake Michigan shoreline from near Michigan City, Indiana to north of Benton Harbor, Michigan. The polar grid spacing of these data fields is about 750 m in range from the radar site and from 7° to 30° in azimuth, over the four radar frequencies. Maximum range is expected to be 30 km or more. These observations would cover the same area where moored current meters (proposed deployment by Dr. Jim Saylor of NOAA) and other instrumentation are to be deployed. The idea here is to have the HF radar fill in the gaps in the point measurements by moorings and buoys as well as providing very near surface current and current shear measurements that are not available from other instruments. We also propose to develop and implement (in collaboration with our research partners) estimates of the current and wind fields using all the measurement data available, e.g. HF radar, moored current meters and acoustic Doppler current profilers, visible, infrared and radar measurements from satellites, buoys, meteorological stations, etc., in a data assimilation process. Finally we propose to participate as a partner in the overall goals of understanding episodic events and cross-margin transport in the Great Lakes and developing a portable data assimilation nowcast/forecast system based on the lower Lake Michigan results. Proposed observations would begin with a pilot experiment in autumn, 1997 or late winter to early spring, 1998 to verify radar performance and test improvements. The major observational effort would be a one to several month experiment period in the late winter to spring time frame in 1999 and 2000 and a small follow up experiment in 2001. Data analysis, nowcast/forecast system development and publication of results would follow. Our proposed component of the overall research program entitled "The Impact of Episodic Events on Nearshore-Offshore Transport in the Great Lakes" has a budget averaging about $100,000 per year (with the two major experiment years having a larger portion of the cost) over five years.