Geophysical Fluid Dynamics: Stratified Flows

Decades of observations of the Earth’s equatorial stratosphere reveal a very regular oscillation where winds alternate between eastern and western directions. Similar phenomena have also been detected in the atmospheres of other planets such as Jupiter or Saturn. It is believed that internal gravity waves, excited by an underlying convective region – the troposphere in the case of the Earth, can propagate in the stably stratified layer and lead to this large scale oscillation through angular momentum deposition. While reduced model of this mechanism have been proposed in the past to investigate this behaviour, in which the action of the waves is taken into account through nonlinear closure models, very few studies have investigated the interaction between convective and stable media due to the very constraining time scale separation. We will present global simulations where both regions are simulated without resulting to any such parameterisation. Through a systemic parametric study, we will discuss how typical properties of the flow generated in the stratosphere evolve, such as its period or mean velocity.

Finally, the question of the regularity of the resulting pattern will be mentioned as it has proven to be relevant in recent years due to the disruption of the observed oscillation on Earth.

Funding acknowledgement

The authors acknowledge support from the Simons Foundation (Simons grant number: SFI-MPS-T-MPS-00007353).