Group seminar on 23. April, 14:15

Temporal variability of waves in the tropical and subtropical upper troposphere

Katharina Holube

The equatorial Kelvin wave is the slowest eastward-propagating mode on the sphere and part of the linear response to tropical heating. Subtropical Rossby waves, which are advected eastward by the background flow, can also influence the Kelvin waves. We have simulated the resonant Kelvin wave excitation by Rossby wave-mean flow interactions with an idealized model. The possible occurrence of this mechanism in the atmosphere is subject of this talk. The Rossby and Kelvin waves are identified in ERA5 reanalysis data using MODES. In the upper troposphere, where the subtropical jet is strong, the temporal variability of the waves is studied because the excitation mechanism requires that the frequency of the Rossby wave-mean flow interactions is close to the Kelvin wave frequency. A cross-spectral analysis of the Kelvin waves with two zonal momentum tendency terms due to Rossby wave-mean flow interactions is performed to evaluate whether these interactions can increase the Kelvin wave energy. Next steps towards assessing the Kelvin wave energy tendencies due to various dynamical processes will also be discussed.