Abstract
The transient response of planetary waves to tropical heating is investigated using a global atmospheric model linearized with respect to basic zonal flows which include both vertical and meridional shear. This work focuses examination on the role of baroclinic instability in generating external-mode motions under the influence of a specified anomalous tropical heating. We found that the process of baroclinic instability of zonal flows can be considered as a cooperative action with tropical heating in the generation of external-mode motions which cause global barotropic-type responses. However, the effectiveness of each process in energy generation is different. For example, the efficiency of generation with tropical heating is greatly reduced in the easterlies and also with decreased longitudinal heating scales. By contrast, the efficiency of generation with baroclinic instability has the opposite tendencies. Hence, the two processes are likely complementary to each other. Other information obtained from the present transient study, but not from previous stationary response studies, is the time scale of generating external-mode motions by the two processes. The time scale of response involving tropical heating as measured by the leveling-off of internal-mode energy level is approximately 10 days. On the other hand, the time scale of response that it takes to produce the solutions close to the steady states under stationary heating is in the range of 20 to 40 days under reasonable energy dissipation rates.
