Seasonal modulation of the El Niño–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 (100°W–50°E; 20–70°N) and the sea surface temperature anomalies (SSTAs) in the tropical Pacific (120–290°E; 20°N–20°S) 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 Niño–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 50°N 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 40–45°N. In January–March, the SLPA pattern associated with the warm minus cold ENSO composite is close to the tropical Northern‐Hemisphere pattern. Copyright © 2003 Royal Meteorological Society.