Abstract
AbstractThe intraseasonal variability of the tropical eastern boundary upwelling region in the Atlantic Ocean is investigated using multiyear mooring and satellite data. Pronounced oscillations of alongshore velocity and sea level off Angola at periods of about 90 and 120 days are observed. Similar spectral peaks are detected along the equator suggesting an equatorial forcing via equatorial and coastally trapped waves. Equatorial variability at 90 days is enhanced only in the eastern Atlantic likely forced by local zonal wind fluctuations. Variability at 120 days is generally stronger and linked to a second equatorial basin mode covering the whole equatorial basin. Besides forcing of the 120‐day variability by equatorial zonal winds, additional forcing of the resonant basin mode likely originates in the central and western tropical North Atlantic. The coastally trapped waves generated at the eastern boundary by the impinging equatorial Kelvin waves that are detected through their variations in sea level anomaly are associated with corresponding sea surface temperature anomalies delayed by about 14 days. Off Angola, those intraseasonal waves interfere with major coastal warm and cold events that occur every few years by either enhancing them as for the Benguela Niño in 1995 or damping them as for the warm event in 2001.
Highlights
The Angolan upwelling system as part of the tropical eastern boundary upwelling system, is a highly productive ecosystem (Binet et al, 2001; Jarre et al, 2015)
The coastally trapped waves generated at the eastern boundary by the impinging equatorial Kelvin waves that are detected through their variations in sea level anomaly are associated with corresponding sea surface temperature anomalies delayed by about 14 days
At the 90-day period, the Angola Current variability is mostly linked to equatorial forcing (Figure 4a)
Summary
The Angolan upwelling system as part of the tropical eastern boundary upwelling system, is a highly productive ecosystem (Binet et al, 2001; Jarre et al, 2015). These extreme coastal warm and cold events usually peak in late austral summer between March and April (Florenchie et al, 2003, 2004; Imbol Koungue et al, 2017, 2019; Lübbecke et al, 2010; Rouault et al, 2007) They are of great socioeconomic importance for the countries of Southern Africa due to their impacts on the marine ecosystem, biological productivity, and fisheries as they modulate the upwelling intensity and upper-ocean mixing thereby setting the upward supply of nutrients (Blamey et al, 2015; Boyer et al, 2001). There might be an impact of IMBOL KOUNGUE AND BRANDT
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