Cooling Index derived from satellite data (1985-2007) in upwelling areas Case: Moroccan coastal upwelling
Benazzouz
Aïssa, National Institute of Fisherie research (INRH-Morocco), benazzouz.inrh@gmail.com
(Presenting)
Demarcq
Hervé, Institute of Research and Developpement (IRD-French), demarcq@ird.fr
Orbi
Abdellatif, National Institute of Fisherie research (INRH-Morocco), orbi@inrh.org
Coastal upwellings are complex biological and physical phenomena, characterised by important fluctuations in time and space. Remote sensing data provides an adequate way to monitor this dynamic.
The main objective is to make available to scientists a synthetic spatio-temporal information based on standard operational products and allowing an easy to use estimate of the upwelling activity.
We use in this work spatial Sea Surface Temperature (SST) data from the NOAA/AVHRR. The main product developed is a thermal upwelling intensity index derived from the SST field that is firstly based on the upwelling presence or absence and that quantifies its intensity according the cross-shore SST gradient.
The results are validated by means of Ekman index calculated from wind data of two meteorological coastal stations of the southern Moroccan coast, Laayoun and Dakhla. Systematic spatial use of data from the QuikSCAT scatterometer also shows that our upwelling index provides a useful complementary observation of the upwelling spatial structure and surface intensity that a wind field alone is unable to provide.
In this way, an upwelling index data set is built, covering 23 years (1985-2007) of weekly data.
The spatial and temporal dynamic of the upwelling along the atlantic moroccan coasts (21-36°N) is described as well as the potential impact of the upwelling intensity on the pelagic stocks in the region.
A classification into four characteristic areas is made according the intensity of the upwelling index which regularly increases from South to North, according to the trade wind gradient.
The zonal seasonality of the index, described from the climatology of the whole data series, is always marked with a maximum of seasonality between 26 and 32° of latitude North and a minimum of seasonality in the South, where the upwelling is strong and quasi permanent.
The inter-annual variability of the index is very consistent in space and do not show any significant temporal trend during the study period except a strong negative anomaly between 1995 and 1997, as a consequence of a strong decrease in the trade winds. This event coincide with a strong negative anomaly on the pelagic fisheries, specially the sardine fishery, both in term of catches and acoustic estimated biomass.
An SST-based upwelling index therefore provides a useful information on the upwelling dynamic to explore the environmental impacts on pelagic stocks in the region.
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