Atmospheric dynamics over northwest Africa and linkages with Sahelian rainfall

The variability of sea level pressure (SLP) anomalies over Northwest Africa (NA) that is, one of the two poles of the NAWA index identified by Paz et al. (2003), and its relationship with Sahelian summer rainfall is investigated during the 1950-1998 period. Significant positive linear correlations of 0.55 (0.60) are found first between spring (summer) SLP anomalies of the southernmost grid-points of the NA pole and Sahelian summer rainfall of the same year. Moreover, by tracking the location of the center of the Azores anticyclone it is argued that the thickness of the Sahara/Sahel thermal low and the latitudinal position of the ITCZ during springtime, are important parameters/ predictors modulating ensuing Sahelian precipitation on different time-scales. Other factors such as natural pentadecadal climate variability, local increase in greenhouse gases concentrations, and sea surface temperature or neighboring oceans might modify global SLP fields and contribute as well to low-frequency Sahelian summer rainfall variability.