Supervisor: Dr Martin Jucker (

There is a direct relationship between the strength of the stratospheric polar vortex and the zonally averaged position of the tropospheric jet stream in both hemispheres. This coupling is apparent on all timescales, from days to centuries. This way, the stratosphere has a downward influence via stratosphere-troposphere interaction which impacts the surface. By exploiting this, both weather predictions and seasonal forecasts can be improved. What is unknown, however, is now this relation works, and possible future changes under climate change are uncertain. This project proposes a process-based approach to tackling the question of how the stratosphere and the troposphere are coupled. By employing a hierarchy of circulation models, it will put several basic mechanisms to the test, as e.g.

  • Is the same cause weakening the stratospheric polar vortex and changes the eddy driven jet position independently?
  • Is the stratosphere a passive or active player in the system?
  • Is the stratosphere only changing the propagation properties of tropospheric waves or does it play a more active role?
  • What is the role of radiative forcing and thus ozone?

These questions will first be addressed with simple statistical models, then with quasi-geostrophic models of the atmosphere, and more and more complex models will be used as the project moves forward.