The upwelling regime off the west Portuguese coast, 1941-2000

The evolution of the upwelling regime off west Portugal between 1941 and 2000 was investigated. Monthly averages of the longshore (meridional) wind component at four coastal stations of the Institute for Meteorology were computed and subject to linear regression analysis. Several comparisons were made among stations until a final regression model was reached. The resulting residuals were checked for the presence of red noise, and pairwise correlation coefficients were estimated for residuals of different stations. To complement this study, monthly sea-surface temperature averages were computed for six regions off west Portugal and subject to a similar procedure. In both analyses, it was concluded that the Portuguese upwelling regime has weakened since the 1940s. The waning of the northerly, upwelling-favourable winds was significant throughout the traditional upwelling season (April–September). Sea-surface temperature showed a steady year-round increase from 1941 onwards, in both offshore (+0.002°C/year) and coastal (+0.010°C/year) regions