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

This study examines the Northern Hemisphere midlatitude circulation response to Arctic amplification (AA) in a simple atmospheric general circulation model. It is found that, in response to AA, the tropospheric jet shifts equatorward and the stratospheric polar vortex weakens, robustly for various AA forcing strengths. Despite this, no statistically significant change in the frequency of sudden stratospheric warming events is identified. In addition, in order to quantitatively assess the role of stratosphere-troposphere coupling, the tropospheric pathway is isolated by nudging the stratospheric zonal mean state toward the reference state. When the nudging is applied, rendering the stratosphere inactive, the tropospheric jet still shifts equatorward but by approximately half the magnitude compared to that of an active stratosphere. The difference represents the stratospheric pathway and the downward influence of the stratosphere on the troposphere. This suggests that stratosphere-troposphere coupling plays a nonnegligible role in establishing the midlatitude circulation response to AA.