China
Africa
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Ocean Oscillation and Drought Indices: Principles
Published in Saeid Eslamian, Faezeh Eslamian, Handbook of Drought and Water Scarcity, 2017
Present-day flow paths of the Agulhas current and the Benguela upwelling system were already established during the Mio-Pliocene around 5 million years ago and may even have been in place as early as 10 million years ago. The introduction of cold water currents on the west coast accentuated the ongoing trend of increased summer drought along the west coast and the Sahelian region, and strengthening high-pressure systems brought drier conditions to the interior. Similarly, there is the upwelling region along the northwest coast of Africa extending from the Canary Island to Cape Verde, which is referred to as the “Canary current systems.” There is however limited detailed study of the relationship existing between upwelling and drought; despite the fact that the region is fairly oceanographically explored, few interpretations or detailed discussions have yet been published. Although upwelling occurs throughout the year, it is however most intense in spring and summer, migrating northward from winter to summer, essentially forming the upwelling period from January to May, with temperature anomalies of almost 7°C.
Atlas of surface currents in the Mediterranean and Canary–Iberian–Biscay waters
Published in Journal of Operational Oceanography, 2022
Justino Martínez, Emilio García-Ladona, Joaquim Ballabrera-Poy, Jordi Isern-Fontanet, Sergio González-Motos, José Manuel Allegue, Cristina González-Haro
The Atlantic domain considered here, is the upper part of the North Eastern boundary of the Atlantic subtropical circulation where three main surface currents systems are often identified: the Canary current, the Azores current and the Portugal current system. An extensive review of the circulation and variability for this region is given in Mason et al. (2005). Basically, it has a marked seasonal variability strongly correlated with the atmospheric forcing. In summer, roughly between April and September, the permanent trade winds blow along the African coast inducing the Canary Upwelling System and are southward along shore winds in the Iberian shelf inducing an upwelling regime in the Portugal and North Western Spanish coasts (Alvarez et al. 2008b, 2011; Santos et al. 2011). During the winter season, the atmospheric circulation close to the Iberian Peninsula weakens and a poleward and along shelf flow develops entering the Gulf of Biscay sometimes denoted as Navidad current (Haynes and Barton 1990; Peliz et al. 2005). This pattern of variability in the Gulf of Biscay is clearly recovered in climatological analysis from drifters (Charria et al. 2013).