Separating the tropospheric and stratospheric pathways of El Niño-Southern Oscillation teleconnections

The El Niño-Southern Oscillation (ENSO) is a major driver of Northern Hemisphere wintertime variability, and generally the dominant factor used in seasonal predictions of wintertime surface climate. Previous studies have suggested that the ENSO teleconnection has both a tropospheric pathway and a stratospheric pathway. Here we attempt to separate the observed surface climate impacts of ENSO into two components: the tropospheric Rossby wave component, and the stratospheric component. We show that ENSO's climate impacts over North America are largely associated with the tropospheric pathway, whereas ENSO's climate impacts over Eurasia are largely associated with the stratospheric pathway. We demonstrate that stratospheric variability (i.e., the strength of the polar vortex) exerts significant influence over the surface impacts of ENSO on intraseasonal timescales; and that even during winters with neutral-ENSO conditions, the influence of stratospheric variability is significant.