A Coastal Niño/Niña Phenomenon Off the Coast of Senegal (West Africa)

Friday, 19 December 2014
Pascal Oettli, Yushi Morioka, Takeshi Doi and Toshio Yamagata, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
A recent discovery, the Dakar Niño/Niña, is introduced, involving a local air-sea interaction in the southern region of the Canary Current, an eastern boundary current in the North Atlantic Ocean.

In the region (20°-15°W, 9°-15°N) located south of the Cap-Vert peninsula (Senegal, Western Africa), Sea Surface Temperature (SST) undergoes a strong seasonal cycle with a minimum variability during boreal late summer/early fall and with a peak in boreal winter when the surface trade-winds are at their peak strength.

The present study identifies that this area is subject to anomalous warming/cooling of the SST in boreal winter, during the period 1982-2011. A close examination of the relationships between the SST and the dynamics of the lower atmosphere reveals the important role played by the surface wind, particularly the meridional component and its angle to the coast. At the interannual time-scale, less (more) intense trade winds in February lead to warmer (cooler) SST in March.

The interannual variability in trade winds (speed and direction) also has an influence on the intensity of the coastal upwelling. These results have implications for a potential impact on the fish abundance and also on the local fishery and economy.

Similar regional warming phenomena have been described in other oceanic basins, such as in the South Atlantic Ocean (Benguela Niño), the southern Indian Ocean (Ningaloo Niño) and the North Pacific Ocean (California Niño). A comparison between the Dakar Niño and the well documented Ningaloo Niño suggests that an important difference arises to be the distinct feedback mechanisms from the ocean into the atmosphere. The Ningaloo Niño (Niña) has significant impacts on regional precipitation in Australia, through changes in SLP anomalies. While the Dakar Niño (Niña) appears to favor the wind-evaporation-SST (WES) feedback, at a local- to regional-scale. The connection between coastal Niño and ENSO is also analyzed.