Revisiting the tropical Atlantic western boundary circulation from a 25-year time series of satellite altimetry data
<p>Geostrophic currents derived from altimetry are used to investigate the surface circulation in the western tropical Atlantic over the 1993–2017 period. Using six horizontal sections defined to capture the current branches of the study area, we investigate their respective variations at both...
Main Authors: | , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2023-03-01
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Series: | Ocean Science |
Online Access: | https://os.copernicus.org/articles/19/251/2023/os-19-251-2023.pdf |
Summary: | <p>Geostrophic currents derived from altimetry are used to
investigate the surface circulation in the western tropical Atlantic over
the 1993–2017 period. Using six horizontal sections defined to capture the
current branches of the study area, we investigate their respective
variations at both seasonal and interannual timescales, as well as the
spatial distribution of these variations, in order to highlight the
characteristics of the currents on their route. Our results show that the
central branch of the South Equatorial Current and its northern branch near the
Brazilian coast, the North Brazil Current component located south of the
Equator, and the Guyana Current have similar annual cycles, with
maxima (minima) during late boreal winter (boreal fall) when the Intertropical
Convergence Zone is at its southernmost (northernmost) location. In contrast, the
seasonal cycles of the North Brazil Current branch located between the
Equator and 7–8<span class="inline-formula"><sup>∘</sup></span> N, its retroflected branch, the northern branch
of the South Equatorial Current to the west of 35<span class="inline-formula"><sup>∘</sup></span> W, and the North
Equatorial Countercurrent show maxima (minima) during late boreal
summer (boreal spring), following the remote wind stress curl strength
variation. West of 32<span class="inline-formula"><sup>∘</sup></span> W, an eastward current (the Equatorial Surface Current, ESC) is observed between 2–2<span class="inline-formula"><sup>∘</sup></span> N, identified
as the equatorial extension of the retroflected branch of the North Brazil
Current. It is part of a large cyclonic circulation observed between
0–6<span class="inline-formula"><sup>∘</sup></span> N and 35–45<span class="inline-formula"><sup>∘</sup></span> W during
boreal spring. We also observed a secondary North Brazil Current
retroflection flow during the second half of the year, which leads to the
two-core structure of the North Equatorial Countercurrent and might be
related to the wind stress curl seasonal changes. To the east, the North
Equatorial Countercurrent weakens and its two-core structure is
underdeveloped due to the weakening of the wind stress. At interannual
scales, depending on the side of the Equator examined, the North Brazil Current
exhibits two opposite scenarios related to the phases of the tropical
Atlantic Meridional Mode. At 32<span class="inline-formula"><sup>∘</sup></span> W, the interannual variability of
the North Equatorial Countercurrent and of the northern branch of the South
Equatorial Current (in terms of both strength and/or latitudinal shift) are
associated with the Atlantic Meridional Mode, whereas the variability of the Equatorial Surface
Current intensity is associated with both the Atlantic Meridional Mode and Atlantic Zonal
Mode phases.</p> |
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ISSN: | 1812-0784 1812-0792 |