Distinguishing stratospheric sudden warmings from ENSO as key drivers of wintertime climate variability over the North Atlantic and Eurasia

Mindful that the observational record is relatively short, and that internal climate variability can be large, the authors here analyze a new 10-member ensemble of integrations of a stratospherere-solving, atmospheric general circulation model, forced with the observed evolution of sea surface temperature (SST) during 1952-2003.

Previous studies are confirmed, showing that El Nino conditions enhance the frequency of occurrence of stratospheric sudden warmings (SSWs), whereas La Nina conditions do not appear to affect it. However, large differences are noted among ensemble members, suggesting caution when interpreting the relatively short observational record. More importantly, it is emphasized that the majority of SSWs are not caused by anomalous tropical Pacific SSTs.