Large-scale tropical convection dynamically influences the tropical and extratropical atmosphere through the propagation of waves. This study investigates how the horizontal and temporal characteristics of tropical convection affect the wave propagation and stability properties of the upper and lower troposphere. A shallow water primitive equation model is utilized in the analysis.
It is well-known that regions of tropical convection are associated with tropical-extratropical wave patterns in the upper troposphere, e.g., the Pacific-North American (PNA) pattern. A fundamental question which has not yet been addressed is: how does the horizontal distribution of localized equatorial heating affect the generation of a Rossby wavetrain? The shallow water model is used to investigate the effect of the horizontal structure and temporal frequency of tropical heating on the propagation of Rossby waves to the extratropics. Another question to be considered is: can this Rossby wavetrain become unstable, or can it induce an instability in the basic state flow in the extratropics?
The barotropic stability properties of the upper and lower troposphere are then investigated for a range of ITCZ strengths and widths. Nieto Ferreira and Schubert (1997) showed that the lower tropospheric ITCZ can be barotropically unstable, in effect causing its own breakdown. The upper troposphere, however, seems to be stable for these cases.The dynamical implications for these results will be discussed.