Seasonal modulation of the El Nino-southern oscillation relationship with sea level pressure anomalies over the North Atlantic in October-March 1873-1996

The seasonal modulation of the relationship between the sea-level pressure anomalies (SLPAs) over the North Atlantic region (100degreesW-50degreesE; 20-70degreesN) and the sea surface temperature anomalies (SSTAs) in the tropical Pacific (120-290degreesE; 20degreesN-20degreesS) is investigated in the northern winter (October to March) from 1873 to 1996, using singular-value decomposition and composite analyses. Both methods show that the pattern of the North Atlantic SLPA associated with the tropical Pacific SSTA in November-December is different from that found in January-March. The surface covered by a significant SLPA is larger in November-December and February-March than in January. In November-December, the warm El Nino-southern oscillation (ENSO) events are associated with negative SLPAs extending from the Hudson Bay to Scandinavia and positive SLPAs over the Azores high. The cold ENSO events are associated with a positive SLPA between Greenland and western Europe. In January, and mainly in February-March, the warm ENSO events are associated with a positive SLPA north of 50degreesN and a negative SLPA extending from the southeastern USA toward western and central Europe. The cold ENSO events exhibit almost reversed SLPA patterns. The change between November-December and January-March is also observed at the hemispheric scale. In November-December, the SLPAs associated with the warm minus cold ENSO composite form a hemispheric north-south dipole pattern with positive (negative) anomalies south (north) of 40-45degreesN. In January-March, the SLPA pattern associated with the warm minus cold ENSO composite is close to the tropical Northern-Hemisphere pattern. Copyright (C) 2003 Royal Meteorological Society.