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  • AGU (American Geophysical Union)  (5)
  • 2005-2009  (5)
Document type
Publisher
Years
Year
  • 1
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    Upper equatorial Atlantic variability during 2002 and 2005 associated with equatorial Kelvin waves (2009)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2022-02-18
    Description: On the basis of moored (35 degrees W, 0 degrees and 23 degrees W, 0 degrees) and satellite observations, we contrast the upper equatorial Atlantic variability during 2002 with those during 2005. Inspection of the interannual boreal summer cold tongue variability revealed a warm (cold) event in 2002 (2005), with relaxed (intensified) winds in the west and the Equatorial Undercurrent (EUC) embedded in a shallower (deeper) thermocline at 23 degrees W. During both years, 2002 and 2005, equatorial Kelvin waves are present in moored observations as 20 degrees C isotherm depth anomalies and dynamic height anomalies. Basin-wide sea surface height anomalies are used to derive an equatorial Kelvin wave mode. The time evolution of this mode represents the basis for a regression analysis to investigate related oceanic variability: Compared to the exceptionally strong wave activity in 2002, equatorial Kelvin waves were generally weaker during 2005. The main effect of equatorial Kelvin waves on zonal velocity anomalies at 23 degrees W, 0 degrees is evident well below the EUC core. Their direct influence on cold tongue sea surface temperature is small, but they are found to affect the equatorial thermocline slope. Prior to the cold tongue onset in 2002 (2005), the presence of equatorial Kelvin waves is associated with a flattened (steeper) thermocline slope that is crucial for the shallowing (deepening) of the EUC core at 23 degrees W and that might precondition the development of the warm (cold) event.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    South Equatorial Undercurrent in the western to central tropical Atlantic (2008)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 35 (L21601).
    Details
    Publication Date: 2019-09-23
    Description: The South Equatorial Undercurrent (SEUC) in the western to central tropical Atlantic is investigated by a combination of shallow floats, with a few acoustically tracked, shipboard current measurements and hydrography. Float trajectories show a well confined SEUC revealing large standing meanders near its western origin. Transports determined from 31 sections across the SEUC increase from 5.6 Sv at 35°W near the western boundary to 10.2 Sv 800 km farther east. Internal recirculations north and south of the SEUC were indicated by the float trajectories and a weak transport reduction farther along its eastward progression is observed. The deep part of the South Equatorial Current carries on both sides of the SEUC interior water masses westward, and supplies almost 5 Sv to the SEUC between 35°W and 28°W, or about half of the SEUC transport in the interior tropical Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GL035753
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Circulation in the central equatorial Atlantic - mean and intraseasonal to seasonal variability (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L07609).
    Details
    Publication Date: 2018-02-19
    Description: The zonal equatorial circulation of the upper 700 m in the central tropical Atlantic is studied based on 11 cross-equatorial ship sections taken at 23–29°W during 1999 to 2005 and on data from a pair of moored Acoustic Doppler current profilers deployed on the equator at 23°W during February 2004 to May 2005. The observations on the equator reveal the existence of two mean westward cores of the Equatorial Intermediate Current below the Equatorial Undercurrent. In contrast to the 2002 moored observations at the same position the intraseasonal variability during the mooring period is dominated by zonal instead of meridional velocity fluctuations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2005GL025498
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Oxygen tongues and zonal currents in the equatorial Atlantic (2008)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2022-02-18
    Description: Equatorial zonal currents and associated oxygen distributions are studied using shipboard hydrographic data, trajectories from isopycnic floats drifting at about 300 m depth, and velocity time series from the upper 1100 m obtained at two equatorial moorings located at 35°W and 23°W. Mean profiles of zonal velocity measured by moored acoustic Doppler current profilers yielded a westward flowing Equatorial Intermediate Current (EIC) below the Equatorial Undercurrent (EUC) at both locations. The EIC consists of two westward current cores at about 250 and 450 m. The upper core of the EIC deepens by about 30 m from 23°W, where it has a mean velocity of 6 ± 2 cm s−1, to 35°W, where the mean is 5 ± 3 cm s−1. The lower core of the EIC is about twice as strong with 12 ± 1 cm s−1 at 23°W and 9 ± 2 cm s−1 at 35°W. The flow below the EUC is characterized by substantial interannual variability. From May to December 2005 a strong, zonally coherent eastward jet occurred at 300 to 350 m depth, found to be an expression of shallow stacked jets superimposed on the mean EIC. Shipboard hydrographic observations in June–July 2006 revealed the existence of a high‐oxygen tongue that can be traced from 35°W to 10°W in the depth range of the eastward jet prevailing during the preceding year. On the basis of an advection‐diffusion balance, it is suggested that the oxygen decrease from 35°W to 10°W within the oxygen tongue is mainly balanced by lateral eddy diffusivity and oxygen consumption, with diapycnal turbulent diffusivity playing only a minor role.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Atlantic Equatorial Undercurrent and associated cold tongue variability (2007)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2022-03-07
    Description: The Atlantic Equatorial Undercurrent (EUC) is studied using a simulation for the period 1990–2002 with a high-resolution ocean general circulation model. Simulated transports of the EUC that supplies the annual mean upwelling in the central and eastern equatorial Atlantic are in good agreement with new transport estimates derived from ship observations, i.e., 19.9 and 14.0 Sv at 35°W and 23°W, respectively. Although the observations are not conclusive concerning the seasonal cycle of EUC transports, the simulated seasonal cycles fit largely in the observed range. The analysis of the EUC variability associated with interannual boreal summer variability of the equatorial cold tongue showed that cold tongue indices, defined either by near-surface temperature or steric height anomalies, are anticorrelated with thermocline EUC transport anomalies: A strong EUC corresponds to low near-surface temperatures and steric heights. The importance of equatorial waves for the cold tongue region is shown: Surface layer transport anomalies at 23°W and 10°W are significantly correlated with both near-surface temperature and steric height anomalies in the equatorial and coastal upwelling regions, indicating an associated eastward phase propagation along the equator toward the African coast where the signal bifurcates into two poleward branches along the coast and is reflected into a westward propagating wave.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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