SYNOPTIC ATMOSPHERIC PATTERNS CONTROLLING THE NORTH-WEST AFRICAN OCEANOGRAPHIC VARIABILITY

The purpose of this paper is to describe the synoptic atmospheric conditions that control the oceanographic variability in the Canary Current Ecosystem (CCE) and how the coastal upwelling process reacts to the atmospheric forcing, recognized as highly variable. We also show that climate indices such as Sea Level Pressure (SLP) and North Atlantic Oscillation (NAO) can both be used to predict the upwelling process. The seasonal and interannual variations of of the Northwest African upwelling between 21°N and 36°N (the African part of the CCE) and its response to large-scale atmospheric variations such as NAO and SLP is studied for the three decades spanning the period 1982-2011 using remote sensing sea surface temperature (SST) and NCEP/NCAR climatic data. To describe and analyze the results, the spatial scenarios of the synoptic and global climatology were investigated and a variety of analysis methods have been applied. It is demonstrated that the intensity of the Azores High over the Eastern Atlantic Ocean determines the strength of the southward upwelling favorable wind especially during the summer to winter transition, better than the NAO index. Furthermore, The estimated cross-correlation between the NAO and the coastal upwelling index derived from SST is weak, due to a lack of correlation. However, the NAO is more adequate than the SLP alone to explain upwelling extreme events, rather than the long-term (5-6 years) upwelling variability observed.