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Time series of high vertical resolution current meter measurements between 600-m and 1800-m depths on the equator in the Atlantic were obtained at two locations, 10° and 23°W. The measurements have a time span of almost 7 years (2000–06) and provide insights into the temporal scales and vertical structure of variability at intermediate depths. Variability in the zonal velocity component records is dominated by semiannual, annual, and interannual fluctuations. At semiannual and annual periodicities, vertical scales are large, on the order of 2000 stretched meters (sm), and show upward phase propagation. In contrast, interannual variability is associated with small vertical scale flows, called equatorial deep jets (EDJs), presenting downward phase propagation most of the time. Fitting a plane wave to these small vertical-scale flows leads to velocity amplitude, vertical scale, and temporal scale estimates of 8 (normalized) cm s−1, 440 sm, and 4.4 yr. However, this plane wave cannot explain all the variability presenting small vertical scales. Indeed, the data suggest that, along with a seasonal cycle of much larger vertical scale, different features with EDJ vertical scale coexist, with the possibility of a semipermanent eastward jet at around 1500 sm. Variability in the meridional velocity component is dominated by intraseasonal fluctuations. In addition, at 23°W, the meridional component shows low-frequency flows that may be due to the interaction of zonal fluctuations with the Mid-Atlantic Ridge.

This paper presents initial results from new velocity observations in the eastern part of the equatorial Atlantic Ocean from a moored current-meter array. During the “EQUALANT” program (1999–2000), a mooring array was deployed around the equator near 10°W that recorded one year of measurements at various depths. Horizontal velocities were obtained in the upper 60 m from an upward-looking acoustic Doppler current profiler (ADCP) and at 13 deeper levels from current meters between 745 and 1525 m. To analyze the quasiperiodic variability observed in these records, a wavelet-based technique was used. Quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands: 5–10, 10–20, 20–40, and 40–100 days. The variability shows (i) a strong seasonality (the first half of the series is dominated by larger periods than the second one) and (ii) a strong dependence with depth (some oscillations are present in the entire water column while others are only present at certain depths). For the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface, while for the others the question of their origin remains open. Phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales. This is especially visible in long-duration events (>100 days) of the zonal velocity component. Comparison with a simultaneous lowered acoustic Doppler current profiler (LADCP) section suggests that some of these flows may be identified with equatorial deep jets. A striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m. These deep current-meter observations would then imply a few months of duration for the jets in this region.

A time series of velocity profile in the upper 150 m of the equatorial Atlantic was gathered at 23W in 2002 within the PIRATA program. It constitutes the first time series of near surface current measurements simultaneous with altimetric data in the equatorial Atlantic. The surface slope anomaly along the equator is computed from satellite altimetry, and, as a proxy for the pressure gradient along the equator, compared with the wind and near surface current data. In a first step, a time series of the surface slope anomaly along the equator in the Atlantic is computed from the 10-year-long TOPEX/Poseidon sea level anomalies. A sensitivity study establishes the robustness of the calculation. Apart from a 15 cm bias, the equatorial sea surface slope anomalies estimated either from TOPEX/Poseidon or from Jason over the 6-month overlap (Feb.–Aug. 2002) do not reveal drastic differences. We produce two sea surface slope anomaly composite time series for 2002 (one with T/P data, the other with Jason data during ...

A detailed description of the frontal structure of major currents and estimates of transport between Africa and Antarctica at 30°E were made on the basis of a finely resolved hydrographic section made during the 1996 Civa-2 cruise. Particular emphasis was put on a refinement of the eastern boundary of the Weddell Gyre by analyzing also supplementary hydrographic data from the 1993 Civa-1 cruise and the best available historical hydrographic data in the Weddell and Enderby Basins. Contrary to the general belief, our results show that the Weddell Gyre extends far beyond 30°E, reaching at least as far east as the Enderby Land promontory (53°E). From this point, westward currents along the Antarctic continental margin constitute the gyre's southern boundary, thus closing the cyclonic circulation of the gyre at its easternmost end. As the most convincing evidence for this refined circulation scheme, significant westward transport south of 65°S has been identified from the Civa-1 acoustic Doppler current profiler data. We have shown also, using an inertial jet model, that the blocked feature of the Weddell cold regime (∼57°S) to the west of 25°E is due to the topographic control of flow by local bathymetry. During the Civa-2 cruise, ∼70% of the Antarctic Circumpolar Current (ACC) was concentrated near the Polar Front (51°S), with surface speeds reaching up to 70 cm s−1. The baroclinic current field in the subpolar area south of the Weddell Front (58°S for Civa-2 and 57°S for Civa-1) is featureless (

International audience; In January/February 2006, a hydrographic section under Jason track 104 across Drake Passage (DP) was performed twice within 3 weeks, on board of the R/V Polarstern. Two LADCPs mounted on the CTD rosette provided the most comprehensive synoptic top-to-bottom observations of directly measured velocity available in the Drake Passage to date, with an estimated error of less than 3 cm s-1. Geostrophic velocities computed from the hydrographic data were referenced to LADCP velocities. The velocity structure of the Antarctic Circumpolar Current (ACC) along the track and its evolution within 3 weeks reflect the frontal branches presented by Barré et al. (2011) and Provost et al. (2011). The repeated section offers two independent transport estimates, computed from the LADCP velocities (145±8.8 and 137.9±10.5 Sv, respectively) and from the adjusted geostrophic velocities (136.6±7 and 129±7 Sv, respectively). Error bars of the transport estimates are small. Contributions of the fronts and eddies to the total transport are modified within 3 weeks but tend to compensate each other. The total transport is reduced by about 10% (15--17 Sv) between the southward and northward journey. Total transport estimations are compared to previous results, in particular the ISOS (International Southern Ocean Study) data, from which the canonical value of 134 Sv has been estimated. Within the uncertainties due to uneven data distribution, no trend is discernible neither in the baroclinic nor total transports from 1975 to 2006.

[1] Near-surface current velocity data from the Pilot Research Moored Array in the Tropical Atlantic at 23°W in the year 2002 were re-examined and compared to simultaneous unpublished velocity data at 10°W, near the surface. Strong 7-day-period fluctuations were observed in the zonal velocity component and in temperature records at 23°W. The large temperature fluctuations near the thermocline depth suggest a vertical velocity component at the same 7-day period. The 7-day-period signals occurred in June/July simultaneously with the seasonal upwelling. The meridional velocity component presented similar spectral contents at 23°W and at 10°W. Two distinguishable quasiperiodic signals were observed in the meridional component at both locations: The first signal occurred in the spring, had a periodicity of about 14 days, was subsurface intensified, and had the characteristics of a mixed Rossby-gravity wave. The second signal occurred three times in the year (once in winter 2001–2002, another in summer, and another during fall 2002), had a periodicity of about 20 days, was strongest close to the surface, and was the result of the passage of tropical instability waves (TIWs). Satellite sea surface temperature (SST) data show the same periodicities as the meridional velocity records, and present a spatial structure in accordance with the TIW-SST signature. The summer of 2002 showed different TIW-SST patterns depending upon location, suggesting the existence of different types of TIWs. Overall, variability in the current meter data for the year 2002 was mainly due to current instabilities, except around boreal spring, where intraseasonal variability in surface winds was strongest.

[1] 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.

This paper presents initial results from new velocity observations in the eastern part of the equatorial Atlantic Ocean from a moored current-meter array. During the "EQUALANT" program (1999-2000), a mooring array was deployed around the equator near 10 W that recorded one year of measurements at various depths. Horizontal velocities were obtained in the upper 60 m from an upward-looking acoustic Doppler current profiler (ADCP) and at 13 deeper levels from current meters between 745 and 1525 m. To analyze the quasiperiodic variability observed in these records, a wavelet-based technique was used. Quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands: 5-10, 10-20, 20-40, and 40-100 days. The variability shows (i) a strong seasonality (the first half of the series is dominated by larger periods than the second one) and (ii) a strong dependence with depth (some oscillations are present in the entire water column while others are only present at certain depths). For the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface, while for the others the question of their origin remains open. Phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales. This is especially visible in long-duration events (>100 days) of the zonal velocity component. Comparison with a simultaneous lowered acoustic Doppler current profiler (LADCP) section suggests that some of these flows may be identified with equatorial deep jets. A striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m. These deep current-meter observations would then imply a few months of duration for the jets in this region.

[1] The hydrological properties and circulation along the TIP (Transport Indian Pacific) section between Java and Australia in September 2000 at the end of the southeast monsoon season are described. It is a reoccupation of the JADE (Java Australia Dynamic Experiment) sections carried out in August 1989 and in February 1992, which encompass the throughflow between the Pacific and the Indian oceans. The net geostrophic transport in September 2000 is of the same order as the August 1989 estimate. The results from the three occupations reveal that the seasonal and inter-annual variability is predominant and during the three cruises the transport evaluations capture the largest variability of the throughflow.

International audience; The hydrological properties and circulation along the TIP (Transport Indian Pacific) section between Java and Australia in September 2000 at the end of the southeast monsoon season are described. It is a reoccupation of the JADE (Java Australia Dynamic Experiment) sections carried out in August 1989 and in February 1992, which encompass the throughflow between the Pacific and the Indian oceans. The net geostrophic transport in September 2000 is of the same order as the August 1989 estimate. The results from the three occupations reveal that the seasonal and inter-annual variability is predominant and during the three cruises the transport evaluations capture the largest variability of the throughflow.

Two hydrographic (θ, S, O2) and trichlorofluoromethane (F-11) sections were carried out between the Australian continental shelf and Indonesia, in August 1989, on board the R.V. Marion Dufresne. The sections lie in the easternmost part of the Indian Ocean where the throughflow between the Pacific Ocean and the Indian Ocean emerges. They allow us to describe the features of the water-property and circulation fields of the throughflow at its entrance in the Indian Ocean. Between the Australian continental shelf and Bali, the Subtropical and Central waters are separated from the waters of the Indonesian seas by a sharp hydrological front, located around 13°30 S, below the thermocline down to 700 m. Near the coast of Bali, upwelling occurs in the near-surface layer under the effect of the southeast monsoon; at depth, between 300 m to more than 800 m, a water mass of northern Indian Ocean origin was present. From the characteristics of the bottom water found in the Lombok basin, the maximum depth of the Java ridge which separates the Lombok basin from the Northwest Australian basin lies around 3650 m. Off Sumba, Savu, Roti and Timor channels a core of low salinity and high oxygen content near-surface water was found in the axis of each channel, which suggests strong currents from the interior Indonesian seas towards the Indian Ocean. The entrance of the deep water flowing in the opposite direction, from the Indian Ocean to the Timor basin, was marked below 1400 m to the sill depth, through an increase of salinity and oxygen content. The flow reversal, observed briefly by a Pegasus direct current profiler in the Timor strait, was located at 1200 m depth. During the southeast monsoon, the net (geostrophic + Ekman) transport calculated on the section Australia-Bali give an estimate of the throughflow between 0 and 500 m of 22 ± 4 × 106 m3 s−1 towards the Indian Ocean, with a concentration of the transport in the upper layers (19 × 106 m3 s−1 in 0–200 m) and near the Indonesian coast, north of 13°30 S. In this region of intense mixing, attempts to make a salinity budget were inconclusive but did not imply any reduction in estimated throughflow transport. Below 500 m the net transport is of the order of the uncertainty. The total estimated transport (0–1900 dbar, deepest sill depth) is 18.6 × 106 m3 s−1 (±7) with a mean temperature of 23°C and a mean salinity of 34.0 psu (but may be as large as 23 × 106 m3 s−1, with mean temperature of 20°C and mean salinity of 34.1 psu).

Dans le cadre du programme HYDROPOL, une série de 7 missions océanographiques a été réalisée dans le Pacifique tropical centre sud (zone economique exclusive de Polynésie Française) entre 1986. Ces missions ont été faites avec le BCBO/MARARA, navire océanographique de 45 mètres équipé pour les études physico-chimiques, courantologiques et biologiques en haute mer. L'objectif essentiel de ces missions était le suivi hydroclimatique du Pacifique central sud par l'étude multiparamètres des propriétés et de la dynamique de la couche océanique 0-500 mètres, étude entrant dans le cadre du programme international TOGA devant couvrir la décennie 1985-1995. Les 7 missions HYDROPOL ont tracé une route triangulaire Tahiti (17,30° S, 150° W), nord des Marquises (6° S- 140° W), Rapa (28° S, 144° W), avec stations hydrologiques tous les 60 à 100 milles (soit 1 degré à 1°30 degré de latitude)

This document shows current measurements which were carried out during two successive mooring operations in the Northeast Atlantic (at 47° N, 10° W) from February 1977 to October 1978. These measurements were part of the European Project NEADS., Ce document présente les mesures de courantométrie qui ont été effectuées au cours de deux mouillages successifs, de février 1977 à octobre 1978, dans l'Atlantique Nord-Est au point 47° N, 10° W. Ces mesures ont été réalisées dans le cadre du projet européen NEADS.

Oceanographical measurement campaigns (streams, flows, temperatures, pressures on the sea bottom), undertaken on the mediterranean shore in the Port-la-Nouvelle area during 1974 and 1975 summers, show that there is not a general flow regime along the coastal zone limited by isobathe 55 m. The large variability of the sea circulation seems to be related to winds regime on one hand, and to surface layers thermal structure evolution on the other land. The appearence of a coastal zone where the water is cold (upwelling — 14 to 15 °C) is very well correlated in the beginning of the summer, when NW winds are present (so called Tramontane). Such a situation disappears with the thermocline deepening. Finally, the spatial low coherence of average flows in surface layers is probably associated with the presence of whirlwinds controlling the coastal hydro dynamical regime. The streams due to tides are practically non-existent, although the changes of pressure on the sea bottom (at 23 and 55 m depths) show essentially that tide waves are present (Δh ≅ 20 to 30 cm). In the contrary, at some n.miles from the coast, more than 50 % of the kinetic energy of flows is concentrated in the inertia oscillations field during all the time that the two-layered system lasts., Les campagnes de mesures océanographiques (courants, température, pression sur le fond), poursuivies sur le littoral méditerranéen dans la région de Port-la-Nouvelle au cours des étés 1974 et 1975, montrent qu’il n’existe pas de régime général de courant dans la bande côtière délimitée par l’isobathe 55 m. La grande variabilité de la circulation marine semble liée au régime des vents d’une part et à l’évolution de la structure thermique des couches superficielles d’autre part. L’apparition d’une bande côtière d’eau froide 14-16 °C (upwelling) est très bien corrélée au début de l’été avec la présence de vents de NW (Tramontane). Cette situation disparaît avec l’approfondissement de la thermocline. Enfin, la faible cohérence spatiale des courants moyens dans les couches superficielles, est vraisemblablement associée à l’existence de tourbillons qui dominent le régime hydrodynamique côtier. Les courants de marée sont pratiquement inexistants bien que les variations de pression sur le fond (à 23 et à 55 m) montrent essentiellement l’existence d’ondes de marée (Δh≅ 20 à 30 cm). Par contre, à quelques milles des côtes, plus de 50 % de l’énergie cinétique des courants se concentre dans le domaine des oscillations d’inertie tant que dure le système à deux couches., Gonella J., Lamy A., Kartavtseff A. Rapport II-5. Hydrodynamique côtière en régime d’été. In: La mécanique des fluides et l'environnement. Prévision et maîtrise de la qualité de l'eau et de l'air. Compte rendu des quatorzièmes journées de l'hydraulique. Paris, 7-9 septembre 1976. Tome 1, 1977.

In this study we objectively analyze simulated equatorial Atlantic Ocean data on seasonal time scales using a technique based on optimal interpolation. The purpose is twofold: (1) to estimate the accuracy of the FOCAL/SEQUAL (Programme Francais Ocean-Climat en Atlantique Equatorial/Seasonal Equatorial Atlantic Response Program) array for mapping large-scale seasonal variations in the depth of the 20" isotherm, and (2) to examine the potential of 20 FOCAL drifting buoys drogued with thermistor chains for enhancing that mapping accuracy. This latter point leads to the development of a heuristic model for drifter motion in order to identify the most favorable time and location for buoy deployments. Results are discussed for a number of assumptions about oceanic variability required by both the optimal interpolation procedure and the drifting buoy model. From these we conclude that with data provided by the FOCAL/SEQUAL array, excluding FOCAL drifters, one can expect to map large-scale seasonal variations in the depth of the 20°C isotherm to within 5 m over about 65% of the equatorial Atlantic. This region of expected 5 m accuracy expands to nearly 90% of the equatorial Atlantic if FOCAL drifters are deployed between 2 and 4OS at 5OW in four quarterly installments of five each. Drifters deployed further to the east or .to the west will be less useful in defining large-scale, low-frequency thermal variations since they do not disperse as widely as do those deployed at 5 OW.