Baroclinic Instability in the Upper Troposphere

Abstract

Observations show that the lapse rate increases upward in the troposphere. Baroclinic instability spectra are presented for the lapse rate increasing linearly upward from small values in the lower troposphere to large values in the upper troposphere. As compared with spectra for a standard atmosphere, growth rates at short wavelengths are reduced, and the wavelength of maximum instability is increased. When the lapse rate is made constant and large in a layer between 400 mb and the tropopause, an additional, rapidly amplifying, baroclinic mode appears, with maximum growth rate at short wavelengths and maximum amplitude in the upper troposphere. Growth rates are large. Similar results are obtained for large shear in the upper troposphere.