Altimetric data to monitor the seasonal and year-to-year variability of the upwelling intensity along the West Africa coasts
Salvatore Marullo(1) , Daniele Iudicone(2) , and Rosalia Santoleri(3)
Via E. Fermi 45,
(2) Stazione Zoologica Anton Dhorn, villa comunale 1, 80121 Napoli , Italy
(3) CNR, ISAC, Via del fosso del cavaliere, 00133 Roma, Italy
At present standard upwelling indexes for the monitoring of coastal upwelling are based on estimate of the wind intensity or wind stress intensity (Ekman transport) along the coast. More complex indexes include the estimate of the Sea Surface Temperature (SST) and/or the wind-driven vertical turbulence.
The actual intensity of the Ekman-like upwellings circulation can be modulated by e.g., the interaction with large scale circulation and the coastal wind, changes in the vertical stratification induced by anomalies in coastal freshwater discharge (runoff). A more direct estimate of the circulation could therefore be useful.
Among the several satellite-based remote sensing of the ocean circulation, altimetric data are the most suitable to monitor the variability of the surface circulation. In particular for the upwelling phenomenology, (wind-induced) geostrophic coastal currents could be a priori monitored.
Here we investigate the possibility of improving our monitoring capability of the upwelling intensity via the inclusion of altimetry-based informations in the definition of upwelling indexes. An upwelling index based on the difference between near-shore and off-shore sea level slope has been defined and applied to altimetric data of the West African Cost. The 15 years time series of Altimeter data together with the corresponding SST time-series has been analyzed to and to investigate the role of local and remote forcing on the upwelling seasonal and interannual variability. The analysis reveals the presences of a strong interannual and coherent signal in both altimetric SLA and SST indices and suggest that only part of the signal induced by local winds