Baroclinic Instability at Short Wavelengths in Vertically Discrete Quasi-Geostrophic and Ageostrophic Models

Abstract

Short wavelength linear baroclinic instability is examined numerically in two quasi-geostrophic models and one ageostrophic model. The growth rate spectra for the ageostrophic model differ little from those of the quasi-geostrophic models in three cases with different arrangements of shear and static stability. In all models and cases, and for 26 vertical levels, peaks of instability were found at very short wavelengths of a few hundred kilometers. These apparently represent spurious critical layer instability appearing at discrete levels, as suggested by Arakawa. They disappear when very high vertical resolution (e.g., 150 levels) is used.