AN EMPIRICAL STUDY OF WIND FACTOR IN LAKE MENDOTA1

Wind blowing across a water surface will transmit momentum to the water and cause a surface current. The ratio of water velocity to wind velocity is called the wind factor. This paper presents observed values of the wind factor obtained as median values and by regression analysis of wind velocity vs. water velocity. The data show that the wind factor is a discontinuous function at a critical wind speed. Water velocity in the surface layers increases with wind velocity until a critical wind speed is reached, and then it decreases. This observation is in agreement with Munk’s (1946) theory of a critical wind speed for air‐sea boundary processes, which yields air‐sea boundary instability for winds exceeding 6.5 m/sec. The observations taken in Lake Mendota yield a critical wind speed of 5.7–6.1 m/sec. The present results were arrived at after a study of 356 observations.