Understanding the Stratospheric Response to Arctic Amplification

Recent studies propose that Arctic sea ice loss and associated warming influence wave propagation into the stratosphere, affecting the winter polar vortex. Through stratosphere-troposphere coupling, this may perturb the winter jet stream and affect surface weather. But the “stratospheric pathway” linking Arctic variability to midlatitude weather extremes is not well understood. For example, studies such as the Polar Amplification Model Intercomparison Project (PAMIP) have not found a robust stratospheric response to Arctic sea ice loss, in strength nor sign.Here, we use an idealised atmospheric modelling framework (Isca) to better understand mechanisms and uncertainties in the stratospheric polar vortex response to Arctic amplification. We use Newtonian relaxation of temperature to a specified equilibrium temperature to simulate northern hemisphere winter, and force the model with an adjustable polar heating. Consistent with previous work, the vortex weakens in response to the imposed heating. Notably, we find a dependency on heating depth; vortex variability and sudden warming frequency reduces with increasing depth. This is relevant to PAMIP given previous work suggesting that atmosphere-only GCMs likely underestimate the depth of sea ice loss-induced atmospheric warming compared to fully coupled ones, and that the Arctic amplification link to midlatitude weather is sensitive to the vertical extent of polar warming. As such, our results should help to improve understanding and reduce biases in such comprehensive models.