The role of the Atlantic Multidecadal Oscillation precondition in the teleconnection of different El Nino-Southern Oscillation types and impacts on the 15°N-15°S South American sector precipitation

The Eastern Pacific (EP) and Central Pacific (CP) El Nino-Southern Oscillation (ENSO) types and their impacts on the tropical North Atlantic (TNA) SST variability and 15 degrees N-15 degrees S South American precipitation during the warm and cold phases of the Atlantic Multidecadal Oscillation (WAMO and CAMO) were evaluated during the 1901-2012 period. The results show more frequent ENSO events during the CAMO. The El Nino (EN) (La Nina [LN]) events, regardless of type (EP or CP), during the WAMO (CAMO) were accompanied by a warming (cooling) in the TNA after its mature phases. In these cases, extratropical teleconnection patterns are established through variations in the Pacific/North America (PNA) teleconnection pattern and are accompanied by variations in the Walker circulation. For the EN (LN) in the CAMO (WAMO), the tropical teleconnections occur predominant, through the Walker cell and the zonal inter-basin gradient, which is intensified due to the SST gradient between the eastern equatorial Pacific (non-neutral anomalies) and the equatorial Atlantic (neutral anomalies). These circulation pattern changes affect the precipitation patterns in the 15 degrees N-15 degrees S South American sector during December-January-February (D(0)JF(+1)) and March-April-May (MAM(+1)). The EP EN (EPEN) events are associated with the intensification of the negative precipitation anomalies in northeastern Brazil (NEB) during the WAMO and in the central part of the Amazon during the CAMO. In the case of CP EN (CPEN) events, the greatest differences between the AMO phases occur during MAM(+1), with reverse sign anomalies over northwestern South America. In the case of LN events, the largest differences occur in NEB, with reduced rainfall in the WAMO, regardless of type EP or CP. The results presented here highlight the role of low frequency oscillations in defining the teleconnection patterns between tropical Pacific and Atlantic Oceans, not discussed previously.