The Probability Density Distribution of the Speed and Horizontal and Vertical Shear of the Zonal-Mean Flow

Abstract

The probability density distribution of the speed, horizontal shear and vertical shear of the zonal-mean wind are computed from a 16-winter NMC dataset in a study designed to complement an earlier study of the planetary-scale wave amplitude probability density distribution. The speed of the zonal wind is found to have a probability density distribution that is unimodal both within the zone of the largest planetary wave amplitude (45°?70°N) and when averaged over the entire midlatitudes (25°?75°N). Unimodal distributions are also found for both the north?south shear of the zonal mean wind and the vertical shear of the zonal mean flow between 300 and 850 mb. Lagged correlations between the zonal mean wind parameters and the wavenumber 2?4 amplitude are computed and found to be small at all lags. This suggests that the temporal variability of the planetary waves in the midlatitudes of the troposphere is not directly connected to the variability in the strength or shear of the zonal mean flow.