How Important Is the Stratospheric Pathway of ENSO for Northern Hemisphere Wintertime Climate Variability? (Invited Presentation)

Tropospheric teleconnections of ENSO are associated with Rossby waves propagating from regions of tropical convective heating. These planetary waves can also amplify into the winter stratosphere, perturbing the stratospheric polar vortex. Extreme perturbations of the vortex, termed sudden stratospheric warmings (SSWs), entirely reverse the stratospheric circulation and can influence surface climate over the North Atlantic and Eurasia. Here we consider this stratospheric pathway of ENSO in both reanalysis and in a 10-ensemble member climate simulation forced with observed sea surface temperatures from 1952-2003. While we confirm previous studies showing an increase in SSWs during El Niño, we see no clear relationship during La Niña. More notably, the occurrence of a SSW during the winter season can overwhelm the anomalies associated with tropospheric teleconnections of ENSO. The stratosphere thus plays a crucial role in Northern Hemisphere wintertime climate variability, but its influence is, to a large degree, independent of ENSO.