Kelvin-Helmholtz Instability in Severe Downslope Wind Flow

Abstract

To test the idea that observed oscillations in severe downslope winds are due to Kelvin?Helmholtz instability, the eigenvalues for the Taylor?Goldstein equation are found for a family of shear flows arising from local hydraulic theory. These two theories, local hydraulic theory and linear Kelvin?Helmholtz theory, provide a reasonable prediction of the period and speed of movement of the wind oscillations but underestimate their growth. The rule-of-thumb critical Richardson number of 0.25 agrees better than the linear theory value found here, 0.1, possibly indicating a nonlinear subcritical instability.