A sharp maximum is frequently observed at night in the wind speed profile below 3000 ft. The wind speed maximum is usually at the top of the nocturnal inversion, is supergeostrophic, and is often associated with extremely large values of wind shear at low levels.It is shown that the characteristic velocity profile tends to promote an orderly growth of the nocturnal inversion. The supergeostrophic wind speeds suggest that an inertia oscillation is induced when the constraint imposed by the daytime mixing is released by the initiation of an inversion at about the time of sunset.

The problem of the approach to the geostrophic wind is solved assuming that the exchange coefficient is proportional to the one‐third power of the rate of dissipation of turbulent energy. Reasonable agreement between the predicted and observed values of the surface stress, surface wind direction, and height of the layer of frictional influence is obtained when the size of the eddies is assumed to become independent of height at a relatively low level. The predicted vertical distribution of exchange coefficient is qualitatively in good agreement with that observed at Leipzig.

No abstract

No abstract

SUMMARYAverages of the wind vector at four times of the day were evaluated for 29 suitable days during the summer of 1951 at Wichita, Kansas, and Oklahoma City. The periodic portion of the wind variation vector is an ellipse at all levels with the major axis approximately in the direction of the wind vector. The amplitude reaches a maximum at 2,500 ft above the ground.The cause of the variation is sought by theoretical methods, first by finding what periodic variations would occur when the eddy viscosity is periodic in time and constant with height, and secondly by finding solutions with the aid of an electronic analogue computer for cases when the eddy viscosity is distributed arbitrarily with height. It is concluded that variations of the type which were observed can occur only when both the average value of the eddy viscosity and the amplitude of its variations decrease rapidly with height above the lowest third of the friction layer.