On the orientation of cloud bands

Abstract

The growth rate of line perturbations in a horizontally stratified saturated fluid is examined for the case of a vertical shear in the mean wind. Certain of these perturbations are unstable for Richardson numbers less than minus two, while perturbations along the direction of the wind shear vector are unstable so long as the static stability is less than zero. It is concluded that cloud bands will tend to be oriented in the wind shear direction.