OBSERVATIONS OF THE VERTICAL STRUCTURE OF THE KEWEENAW CURRENT, LAKE-SUPERIOR

The vertical structure of the Keweenaw Current, on the south shore of Lake Superior, is studied using data from an autonomously profiling cu rrent meter moored 2 km offshore (depth = 100 m). Vertical profiles of temperature, current speed, and current direction show current direct ion strongly aligned east-west with the topographic contours, with cur rents below 50 m depth most frequently flowing eastward at speeds of 6 -12 cm/s, and those above 50 m depth flowing sometimes eastward and so metimes westward at speeds of 10-20 cm/s. Principal component analysis on profiles of eastward velocity reveals two vertical modes which hav e approximately the barotropic and first baroclinic modal form. The do minant ''barotropic'' mode contains 90% and 82%, respectively, of the eastward velocity and temperature variances. Strong occurrences of thi s mode (full-water-column eastward flows with speeds up to 37 cm/s) ar e related to strong increases in the temporal integral of longshore wi nd stress, consistent with coastal jet theory. The ''baroclinic'' mode , containing 6% of the eastward velocity variance, is dominant only du ring periods of weak longshore wind stress. Its 4-day period is compar able with a typical interval between atmospheric frontal disturbances.