Effects of Sudden Stratospheric Warmings and Quasi-biennial Oscillation on El Nino Teleconnections

The effects of the tropical Pacific El Nino-Southern Oscillation (ENSO) phenomenon are communicated to the rest of the globe via atmospheric teleconnections. Traditionally, ENSO teleconnections have been viewed as tropospheric phenomena, propagating to higher latitudes as Rossby waves. Recent studies, however, suggest an influence of the stratosphere on extra-tropical ENSO teleconnections. The primary modes of variability in the stratosphere are sudden stratospheric warmings (SSWs) and the tropical quasi-biennial oscillation (QBO). Here, we conduct 10-member ensemble simulations with a stratosphere-resolving atmospheric general circulation model forced with observed sea surface temperatures during 1952 - 2001 to examine the effects of SSWs and the QBO on the extra-tropical El Nino response. We find that SSWs have a large impact on the winter tropospheric response. During El Nino winters with SSWs, the polar stratosphere warms and these temperature anomalies propagate downward to the surface where they are associated with increased sea-level pressure over the Arctic and cooling over northern Eurasia. During El Nino winters without SSWs, the stratosphere and upper troposphere cool but these temperature anomalies do not propagate downward to influence the surface. The QBO further modulates these teleconnections primarily in winters without SSWs.