ENSO impact on midlatitude circulation patterns in future climate change projections

The remote influence of the leading mode of interannual variability in the Tropics, the El Nino/Southern Oscillation (ENSO), on the northern hemispheric midlatitude circulation in future climate is investigated. For this, IPCC SRES scenarios of the latest version of the coupled climate model ECHAM5/MPI-OM are used. In ensembles of future climate change projections it is found, that a changing state of ENSO with increased variability has a pronounced influence on the dominant midlatitude circulation pattern, namely the Pacific North America (PNA) pattern and the North Atlantic Oscillation (NAO). More explicitly, in the 21st and 22nd century, a positive (negative) phase of ENSO is more likely followed by a positive (negative) PNA index and negative (positive) NAO index than it is observed in the 20th century. Correlation coefficients between the winter mean Nino3.4 index and the NAO index increase substantially from the 20th century.