On the Wavelength of Maximum Baroclinic Instability

Abstract

Abstract A four-level quasigeostrophic model of a baroclinic atmosphere is used to examine the instability of short (∼2000 km) baroclinic waves. It is determined that only a slight decrease in the low-level static stability or increase in the low-level wind shear relative to the stale stability and wind shear in the middle and upper troposphere can mean the difference between the maximum growth rate occurring at a wavelength of 4000 km (∼wavenumber 7) or 2000 km (∼wavenumber 15). Similar changes of static stability in the upper troposphere relative to the middle and lower troposphere have very little effect on the growth-rate spectrum. This effect of vertical variations in the static stability and wind shear on the growth-rate spectrum is consistent with the structure of the short wavelengths. Wavelengths 4000 km extend through the depth of the troposphere. Therefore, changes in the static stability of the basic zonal flow near the earth's...