The response of the coastal boundary layer to wind and waves: Analysis of an experiment in Lake Erie

Abstract

Wind, waves, currents, and water levels were measured near Lake Erie's southeastern shore during fall 1981. Data were recorded continuously at a wave research tower 6 km offshore at three Waverider buoys deployed around the tower and at three current meter moorings along a transect between the tower and the shore. During four storm episodes, wave and current data were also recorded from a dense array of instruments along a transect across the surf zone. A statistical analysis of the deep water data was performed, and histograms of meteorological parameters, wave parameters, and water level slope were plotted as a function of wind direction. The atmospheric boundary layer was usually unstable; on the average, the water was 2–3°C warmer than the air. This was true for all wind directions. At the tower the highest waves were associated with the greatest fetch distances to the WSW and WNW directions. The longest period waves were also associated with these wind directions. The mean water level slope was opposite the mean wind direction. This discrepancy is most likely due to small leveling errors in the water level gages. The variation of currents with wind direction was also examined. The currents are strongest when the winds are from the west, the quadrant with the strongest wind speeds. However, there are strong currents (5–10 cm/s) for all wind directions. The deep water currents are basically shore parallel, with the onshore/offshore component averaging 39% of the root mean square longshore component. Analysis of the four storm episodes reveals the influence of the offshore currents on the flow regime within the surf zone. Quantitative estimates of the longshore momentum balance outside the surf zone show wind stress and pressure gradient to be the dominant dynamic terms. Inside the surf zone, the radiation stress, wind stress, and bottom stress terms all have comparable effects and are usually larger than the acceleration and pressure gradient terms. In between, there is evidence of longshore flow reversals in the breaker zone and the effect of seiche‐induced offshore currents on the near‐shore flow regime.

The role of wave‐current interaction in Lake Erie's seasonal and episodic dynamics

“…These were of larger or comparable values than in the nearshore regions (Figure i) and are at the same order as the observed by Schwab et al . [] in nearshore Lake Erie during a fall episode in 1981.…”

“…In addition, previous observations and model simulations have recognized the significances of the radiation stress in shallow water dynamics [e.g., Sheng and Liu , ; Orescanin et al ., ; Wargula et al ., ]. However, even though wave‐driven processes have been consistently emphasized in the lakes' nearshore dynamics in earlier observations [e.g., Schwab et al ., ; Rao and Schwab , ], the radiation stress was often ignored in previous modeling studies [e.g., Beletsky and Schwab , ; Beletsky et al ., ; Niu et al ., ].…”

Evaluation of the TOPEX/POSEIDON altimeter system over the Great Lakes

“…On the timescale of 1 to 5 days the lakes respond to varying levels of wind stress resulting from passing weather systems causing them to always be in a transient state [Csanady, 1973]. Considerable research has been conducted on wind-driven circulation patterns [e.g., Csanady, 1968Csanady, , 1972Csanady, , 1973Schwab et al, 1984] and the resulting elevation differences across the lakes. The magnitude of the wind setup, resulting from persistent winds blowing across the lakes, will vary depending on the configuration of the lake.…”

Wind‐driven surface transport in stratified closed basins: Direct versus residual circulations

“…These basins and their coastal regions may then serve as models of the coastal ocean. Results from Lake Tahoe suggest that experiments and models of these well-monitored systems, as reported bySchwab et al [1984], could increase our understanding of basin and coastal dynamics by emphasizing, rather than minimizing, the role of horizontal variations in the wind.6. SUMMARY AND CONCLUSIONSA numerical model has been used to determine the winddriven circulation in a moderately large, stratified, closed basin.…”