Baroclinic Instability of Easterly Jets with Applications to the Summer Mesosphere

Abstract

Abstract anally and seasonally averaged zonal wind fields in the summer mesosphere are unstable in the Charney-Stern sense, with a primarily baroclinic component. Two-dimensional stability analyses show peaks in the unstable wave growth spectrum at zonal wavenumbers 2–4, with periods of 1.4–3 days, for a variety of basic state flows. Wavenumbers of peak growth are consistently lower for the two-dimensional analyses than for the one-dimensional analyses, with the lowest wavenumber peaks found for the basic state flows with the smallest latitudinal scale. For strongly baroclinic basic state flows, wave growth was inhibited by introducing stronger latitudinal variations in the basic state flow; however, for marginally unstable flows, stronger latitudinal variations slightly enhance the peak growth rates. The strong thermal damping in the mesosphere reduces growth rates by 20–60% of the damping rate, but has little effect on the wave structure. The primary significance of the thermal damping is that basic sta...