6533b870fe1ef96bd12cfbac

RESEARCH PRODUCT

Variabilité intra-saisonnière et multi-décennale de la téléconnexion entre les pressions de surface (100°W–50°E ; 30°–70°N) et les ENSO/LNSO (1873–1996)

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Abstract The relationships between an index of the NINO3.4 region and the wintertime sea level pressure (hereafter SLP) anomalies on the extratropical North Atlantic and the bordering areas (100°W–50°E; 30°–70°N) are studied for 1873–1996. This study emphasizes the need of a careful pooling of months and the multi-decadal variability of the ENSO/LNSO influence on the extratropical North Atlantic. We calculate the mean monthly climate anomalies for the 20 warmest and the 20 coldest NINO3.4 (170°–120°W; 5°N–5°S) years from October to March. The composite of SLP anomalies for the 20 warmest NINO3.4 years shows an anomalous trough centered near 30°W in November–December, and positive (respectively negative) SLP anomalies north (respectively south) of 50°N in January, and over Northeast Canada and Greenland (respectively from Cape Hatteras to Scandinavia) in February–March. The composite for the 20 coldest NINO3.4 years shows an anomalous ridge from Greenland to Western Europe in October–December, and then positive (respectively negative) SLP anomalies south (respectively north) of 50°–55°N in January–March. The positive SLP anomalies increase near 35°–40°N in February–March. ENSO/LNSO teleconnections on the extratropical North Atlantic are then highly different, and sometimes completely reversed, between the months of November–December and those of January–March. In November–December, the relationships seem stronger at the beginning and at the end of the 20th century. In January–March, the intensity of teleconnections is less variable even if the SLP anomalies associated with the warm events increase in the absolute sense from the beginning of the 20th century and shift slightly southward.