On the Instability of Asymmetric Jets

Abstract

A linear, quasi-geostrophic, channel model is used to study the instability of zonally independent jets on a midlatitude beta plane. The jets possess strong horizontal as well as vertical wind shear. The most unstable normal mode solution for a symmetric jet is compared to corresponding solutions for asymmetric jets, where the maximum winds are skewed toward the cyclonic side. A significant increase in the growth rate is found for the asymmetric jets, the rate increasing with the amount of skew. In addition, skewing the jet results in raising the maximum of the eddy momentum flux to the top of the channel, compared to maxima at lower levels for the symmetric jet solution. Thus, the use of more realistic, cyclonically skewed jets as basic states for instability studies may result in more realistic growth rates as well as in more realistic eddy flux patterns. Results qualitatively similar to those of Brown (1969) are found in that a weak, secondary maximum in the growth rate curve shows up for short, shallow modes for some of the asymmetric jet solutions.