Abstract

It is now well established that the El Niño/Southern Oscillation (ENSO) impacts the climate of middle and high latitudes. Unanswered questions remain, however, and their resolution is central to assessing and fully harvesting the atmospheric predictability inherent in the ENSO phenomenon. Among these questions are the sensitivity of the extratropical response to the annual cycle, the nonlinearity of that response with respect to the sign and amplitude of tropical sea surface temperature (SST) anomalies, and the further sensitivity of the response to differences in the SST anomaly patterns that distinguish one El Niño event from another. Beyond these problems of seasonal to interannual variability, it is also important to understand multidecadal-scale variations of ENSO impacts and to assess their origins.

Our inquiry into these problems begins with an analysis of the last half-century of observed circulation data, using the upper tropospheric flow patterns to identify the teleconnections that link the tropics and the extratropics during ENSO. Several new aspects of the observed teleconnection behavior are highlighted; however, the data archive is undoubtedly too brief to offer a complete or even an accurate sample of the spectrum of atmospheric sensitivity to ENSO. Nor is it likely that the full spectrum of tropical SST variations themselves have been sampled by observations. We thus provide additional analyses based on the results of atmospheric general circulation model experiments that have been forced either with the recent 50-year record of observed global SST variations or with idealized SST anomalies.