Upper Level Barotropic Instability in the Tropics.

The structure of barotropically unstable disturbances in the tropics was examined with a two-level quasi-geostrophic model. The forecast equations were linearized and non-dimensionalized and the most unstable mode was found numerically by use of the initial value technique. The wind profile U sub j a sub jU sub 0sech squared yL was used. Simple CISK type heating was introduced to determine its effects on the growth of the waves. The jet wind profile was more unstable with easterly flow than westerly flow when no heating or friction was present. When the jet profile was present only at the upper level, the ratio of the disturbance amplitude at the lower level to the disturbance amplitude at the upper level decreased toward the equator. When the heating rate was not large enough to increase the growth rate, the amplitude ratio remained small. As the heating rate becomes larger, the ratio increases to a value larger than 1.