Equatorial adjustment in the eastern Atlantic

Moore, D. W.; Hisard, Philippe; McCreary, Julian P.; Merle, Jacques; O’Brien, James J.; Picaut, Judicaël; Verstraete, Jean-Marc; Wunsch, Carl

doi:10.1029/gl005i008p00637

Cited by 103 publications

(47 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The summertime shoaling of the eastern thermocline is part of a basinwide adjustment to the strengthening easterly winds. Previous studies suggest that the large part of the seasonal upwelling in the Gulf of Guinea is remotely forced by the wind changes in the western equatorial Atlantic via equatorial Kelvin waves (Moore et al 1978;Adamec and O'Brien 1978;McCreary et al 1984;Busalacchi and Picaut 1983).…”

Section: B Seasonal Cyclementioning

confidence: 99%

Some Overlooked Features of Tropical Atlantic Climate Leading to a New Niño-Like Phenomenon*

2006

View full text Add to dashboard Cite

The Atlantic Niño, an equatorial zonal mode akin to the Pacific El Niño-Southern Oscillation (ENSO), is phase-locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the Gulf of Guinea. A suite of satellite and in situ observations reveals a new mode of tropical Atlantic variability that displays many characteristics of the zonal mode but instead peaks in November-December (ND). This new mode is found to be statistically independent from both the Atlantic Niño in the preceding summer and the Pacific ENSO. The origin of this ND zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial Atlantic.In November the equatorial easterly winds intensify for the second time, increasing upwelling and lifting the thermocline in the Gulf of Guinea. An analysis of high-resolution climatological data shows that these dynamical changes induce a noticeable SST cooling in the central equatorial Atlantic. The shoaling thermocline and increased upwelling enhance the SST sensitivity to surface wind changes, reinvigorating equatorial ocean-atmosphere interaction. The resultant ocean-atmospheric anomalies are organized into patterns that give rise to positive mutual feedback as Bjerknes envisioned for the Pacific ENSO. This ND zonal mode significantly affects interannual rainfall variability in coastal Congo-Angola during its early rainy season. It tends to further evolve into a meridional mode in the following March-April, affecting precipitation in northeast Brazil. Thus it offers potential predictability for climate over the Atlantic sector in early boreal winter, a season for which local ocean-atmosphere variability was otherwise poorly understood.

show abstract

Section: B Seasonal Cyclementioning

confidence: 99%

Some Overlooked Features of Tropical Atlantic Climate Leading to a New Niño-Like Phenomenon*

2006

View full text Add to dashboard Cite

show abstract

“…This intensification might be related to the northerly wind biases along the African coast, which peaks about 2-3 months before the maximum SST bias. Many studies have also suggested that wind stress along the equator exerts a crucial influence on the coastal region of southwestern Africa via Kelvin waves for both interannual (Florenchie et al 2004, Rouault et al 2007, Lubbecke et al 2010) and seasonal variability (Moore et al 1978;Yamagata and Iizuka 1996).…”

Section: Southeast Atlantic Biasesmentioning

confidence: 99%

Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation

et al. 2011

View full text Add to dashboard Cite

Most coupled general circulation models (GCMs) perform poorly in the tropical Atlantic in terms of climatological seasonal cycle and interannual variability. The reasons for this poor performance are investigated in a suite of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory (GFDL) coupled GCM. The experiments show that a significant portion of the equatorial SST biases in the model is due to weaker than observed equatorial easterlies during boreal spring. Due to these weak easterlies, the tilt of the equatorial thermocline is reduced, with shoaling in the west and deepening in the east. The erroneously deep thermocline in the east prevents cold tongue formation in the following season despite vigorous upwelling. The Bjerknes feedback further amplifies the SST biases and prolongs their effect in boreal summer when equatorial winds are close to observations. It is further shown that the surface wind errors are due, in part, to deficient precipitation over equatorial South America and excessive precipitation over equatorial Africa, which already exist in the uncoupled atmospheric GCM. Additional tests indicate that the precipitation biases are highly sensitive to land surface conditions such as albedo and soil moisture. This suggests that improving the representation of land surface processes in GCMs offers a way of improving their performance in the tropical Atlantic.The weaker than observed equatorial easterlies also contribute remotely, via equatorial and coastal Kelvin waves, to the severe warm SST biases along the southwest African coast. However, the strength of the subtropical anticyclone and along-shore winds also play an important role.3

show abstract

“…Upwelling is a physical process that results in the migration of rich surface waters that promote the proliferation of plankton and therefore fish. Several hypotheses have been proposed to explain this phenomenon along Côte d'Ivoire coastline (Ingham, 1970;Moore et al, 1978;Severain et al, 1982;Picaut, 1983). The most obvious manifestation of a coastal upwelling is the formation of the temperature gradient between the coast and the offshore.…”

Section: Discussionmentioning

confidence: 99%

Seasonal Variation of Thermocline Depth: Consequence on Nutrient Availability in the Ivorian Coastal Zone

Jean-Baptiste

Hervé

Jeanne

et al. 2017

ESJ

View full text Add to dashboard Cite

Faced with the threat of overfishing in Africa, this study was initiated in the coastal zone of Côte d'Ivoire to understand the nutrients availability as function of variation in the depth of thermocline. Data from the ocean bank, World Ocean Atlas (WOA), were used in the ODV software during the twelve months of 2009 taken at 5.5°W/4.5°N (station coordinates). ODV software has allowed to make seasonal analysis, from vertical profiles and latitudinal analysis from the coast toward the sea through some parameters such as temperature, nitrate, phosphate and oxygen. The depth of thermocline, nitracline, phosphacline and oxycline was determined by the seasonal analysis. To evaluate the enrichment intensity of coast towards the sea, latitudinal analysis was investigated using the section profiles (1°S/5°N European Scientific Journal November 2017 edition Vol.13, No.33 ISSN: 1857 -7881 (Print) e -ISSN 1857-7431 216 coordinates). The main results have shown not only the variation in the depth of the thermocline, but also the variation of nitracline, phosphacline and oxycline at different marine seasons. During the cold season, there was an ascent of the thermocline over the surface of water and a strong enrichment from the coast to the sea especially in August. While in hot season, the thermocline was lower and its stability has favoured the stratification of the water column, which prevents the enrichment of the oxygenated surface layer. Analysis of relationships shows that nutrient elements and oxygen change polynomially with temperature.

show abstract

Equatorial adjustment in the eastern Atlantic

Cited by 103 publications

References 6 publications

Some Overlooked Features of Tropical Atlantic Climate Leading to a New Niño-Like Phenomenon*

Some Overlooked Features of Tropical Atlantic Climate Leading to a New Niño-Like Phenomenon*

Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation

Seasonal Variation of Thermocline Depth: Consequence on Nutrient Availability in the Ivorian Coastal Zone

Contact Info

Product

Resources

About