Response of Northern Hemisphere Midlatitude Circulation to Arctic Amplification in a Simple Atmospheric General Circulation Model

Abstract:

There is an increasing body of observational and modeling evidence that Arctic Amplification (AA) might strongly impact both the weather and climate, not only in the Arctic region, but also remotely in Northern Hemisphere midlatitudes. However, discrepancies in atmospheric circulation response exist among different model integrations. 

To investigate the robust circulation response in both the troposphere and stratosphere, we make use of a dry primitive equation model with a simple representation of the stratospheric polar vortex. We have found that, with an imposed AA forcing, the tropospheric jet shifts equatorward and the stratospheric polar vortex weakens, which is in good agreement with previous studies. Despite the weakening of the stratospheric polar vortex, we have found no statistically significant change in the frequency of sudden stratospheric warming events. Furthermore, in order to quantitatively assess the role of stratosphere-troposphere coupling, we isolate the tropospheric pathway by nudging the stratospheric zonal mean state towards the reference state. With the nudging method and thus an inactive stratosphere, in response to AA, the tropospheric jet is still found to shift equatorward, but by only about half the magnitude compared to that of an active stratosphere. The difference represents the stratospheric pathway and the downward influence from the stratosphere on the troposphere. This suggests that stratosphere-troposphere coupling plays a non-negligible role in establishing the midlatitude circulation response to AA.