Linear barotropic instability of the tropical easterly jet on a sphere

Abstract

A barotropic global spectral model is used to determine the linear divergent barotropic instability characteristics of the tropical easterly jet by applying an initial value technique. These characteristics are compared with those on a beta plane, in order to identify the important effects of the spherical geometry an unstable modes. The increase in the growth rate of unstable modes on the sphere is due to the absence of lateral walls. The primary and secondary maxima of the wave amplitude are located at 3.5° and 18.5°N, respectively. It is found that the spherical geometry plays an important role in locating the wave amplitude maximum and the angular momentum transports by the wave. There exists a strong correlation between the two wave amplitude maxima and the extrema of q_μ/αq. It is seen that the midlatitude westerly jets stabilize the easterly jet. The influence of westerly jets is investigated in terms of the overreflection of the meridional propagation of waves from critical latitudes.