Abstract
Mechanisms of the interannual variability of upwelling onset dates on the Petite-Cote of Senegal are investigated using daily NEMO model data outputs and NOAA ocean surface temperature observations (OISST). We first determined the phenology (onset dates, end dates, duration and occupied area of the upwelling) over the Petite-Côte located in south of the Senegalese coast. Our results show that upwelling in the Petite-Côte starts on average on 03-December (with a standard deviation of 13 days) and ends on average on 13-June (with a standard deviation of 11 days). Upwelling lasts, on average, 6 months in the region. The maximum upwelling intensity is noted on 15-May and the maximum occupied area exhibits a February-May plateau. We then performed a composite analysis based on the earliness of the upwelling setup dates to understand the mechanisms involved. Our results show that for the earliest upwelling years, we note a strengthening of the vertical velocities 3 weeks before the onset of the upwelling but we note especially an abnormal intensification of the coastal jet. The latter seems to be the initiator of the early onset of the upwelling in the region. These reinforcements are associated with a significant decrease in surface temperature (SST) and an intensification of northerly trade winds. Key words: Upwelling, phenology, Senegalese coast, petite-côte.
Highlights
The Senegalese upwelling is the southern part of the Canary Islands upwelling system, which is one of the four major upwelling systems in the world, along with the Benguela in South Africa, California in North America and Peru-Chile (Humboldt) in South America
This study focuses on the analysis of physical oceanic and atmospheric parameters that initiate the upwelling from the regional circulation model (NEMO) and is part of the general problem of understanding the Senegalese upwelling in terms of phenology, variation of basic upwelling parameters (SST, Wind, Currents, Mixing layer, Thermocline) and the effect of possible changes in atmospheric circulation on this part of the Canary Islands system
One of the most important parameters for understanding coastal upwelling is the study of wind speed and direction
Summary
The Senegalese upwelling is the southern part of the Canary Islands upwelling system, which is one of the four major upwelling systems in the world, along with the Benguela in South Africa, California in North America and Peru-Chile (Humboldt) in South America. Despite a relatively small surface area, less than 1% of the ocean surface, these regions are known for their intense biological productivity This richness is mainly due to the trade winds that blow parallel to the coast, generating coastal upwelling (Rebert, 1978; Roy, 1989). Coastal and off-shore upwelling result from these northeasterly winds, which drive a zonal Ekman transport under the action of the Coriolis force (Jacox et al, 2018). This transport is divergent, strong at the coast, and in the ocean interior over a distance depending on latitude (Faye et al, 2015).
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