How non-linear is the response of the polar vortex to forcing from large volcanic eruptions?


Large tropical volcanic eruptions emit sulfur into the stratosphere, which forms sulfate aerosols that cool the global surface and warm the tropical lower stratosphere. Observations indicate that this leads on average to a strengthening of the Northen hemispheric stratospheric polar vortex, and ultimately to circulation changes down to the troposphere that cause a winter warming over Northern Eurasia. Until recently, it was assumed that most state-of-the-art climate models do not represent this circulation effect. However, in a recent paper (Bittner et al., GRL, 2016), we have shown that current climate models on average do simulate a vortex strengthening. But this effect is significant only for very strong eruptions. The task in this master project will be to understand if the response of the vortex depends non-linearly on the volcanic forcing. For this purpose we suggest to perform and analyze a number of climate model simulations with idealized volcanic forcings of different strengths.


Supervisors: Hauke Schmidt and Claudia Timmreck