Understanding mechanisms of Rossby wave propagation in the Southern Hemisphere

Stationary Rossby waves forced by the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) have an important role in Southern Hemisphere weather and climate, including promoting Australian rainfall variability and driving Antarctic sea ice variations. However, the dynamics of these teleconnections are not fully understood. In this seminar, I will explore the mechanisms involved in the establishment of these tropical to extratropical teleconnections during austral winter using a set of large-ensemble experiments with prescribed equatorial diabatic heating anomalies. In the first part of this talk, I will explore the mechanisms that enable a stationary Rossby wave to overcome a barrier to wave propagation where the meridional gradient of absolute vorticity becomes negative. In the second part, I will examine the mechanisms behind the asymmetric extratropical height response to westward-shifted ENSO events (like what occurs during La Niña and central Pacific El Nino) and eastward-shifted ENSO events (like canonical or eastern Pacific El Niño). The relative importance of non-linear effects will be assessed by contrasting the comprehensive experiments with results from a simple linear model.