On the relationship between ENSO diversity and the ENSO atmospheric teleconnection to high-latitudes

Abstract

The El Nino-Southern Oscillation (ENSO) has experienced changes in its properties since the 1990s, particularly increased occurrence of Central Pacific El Nino events. These events have influenced atmospheric circulation in the mid to high-latitudes of both hemispheres through atmospheric teleconnection. Here it is shown that, in the Northern Hemisphere, the planetary circulation response to the Eastern Pacific (EP) event in boreal winter is associated with Rossby waves propagating poleward and is mostly confined to the Pacific region, while the Central Pacific (CP) event induces a negative phase of Arctic Oscillation (AO)-like circulation pattern at planetary scale. In the Southern Hemisphere (SH), the difference between the circulation patterns associated with the two types of El Nino in austral summer is rather small and the response of the tropospheric circulation consists of an Antarctic Oscillation (AAO)-like negative phase pattern. In the SH, the circulation response to CP Nino lasts longer than that to EP Nino. In particular, during EP Nino the composite circulation anomalies reverse sign from austral summer to winter, which is not the case during CP event. This adds an interhemispheric asymmetry dimension to the ENSO atmospheric teleconnection in the high-latitudes in relation to ENSO diversity. These changes in the circulation are associated with surface air-temperature anomalies that have the potential to exacerbate observed long-term trends. A subgroup of CMIP5 models that realistically simulate both ENSO nonlinearity (diversity) and the AO and AAO-like patterns are analysed, showing that in the warmer climate, the circulation response in the high-latitudes to both types of events is amplified in both hemispheres.