Group seminar on 4. July, 14:15 CET

Excitation of equatorial waves by subtropical wave-wave and wave-mean flow interactions

Katharina Holube

The Kelvin wave is one of the wave types occurring in the tropical atmosphere, where it contributes significantly to large-scale tropical variability as it propagates eastward. While Kelvin waves are mainly generated by atmospheric convection, their excitation by higher-latitude processes, especially dynamical processes in the subtropics, is of interest. In my Master's thesis colloquium, I describe how interactions between subtropical Rossby waves and the zonal mean flow serve as an excitation mechanism of Kelvin waves. The mechanism is simulated with a numerical model that solves the rotating shallow-water equations on the sphere and has the Kelvin wave as a prognostic variable.  External wave forcing is applied to shift the Rossby waves eastward. The wave-mean flow interactions are separated into components to explain the Kelvin wave excitation as a resonance mechanism. Furthermore, Kelvin waves can be excited by wave-wave interactions of subtropical Rossby waves. The presented excitation mechanism is one example for interactions between waves at different latitudes.