Robert L. Molinari

The arrival of recently formed Labrador Sea Water in the deep western boundary current at 26.5 °N

The Deep Western Boundary Current (DWBC) of the North Atlantic is a principal conduit between the formation region for Labrador Sea Water (LSW) and the oceanic interior to the south. Time series (1985–1997) of hydrographic properties obtained in the DWBC at 26.5°N show that prior to 1994, temperature, salinity, and transient tracer properties within the LSW density range showed little indication of recently formed parcels. Properties characteristic of a newer version of LSW (cooler, fresher, and higher tracer concentrations) were observed beginning in 1994 and continuing through 1997. Longer time series of temperature and salinity, developed from a regional data base, show both the 1994 and a 1980–1981 event in the Abaco region. Both events are consistent with anomalies in the Labrador Sea that occurred some 10 years earlier. The 10-year transit time from the Labrador Sea to 26.5°N is less than the 18-year transit time inferred from earlier studies.

Upper layer circulation in the western tropical North Atlantic Ocean during August 1989

Shipboard acoustic Doppler current profiler velocity measurements and profiles of temperature, salinity, and dissolved oxygen measurements are used to map the flow field above the σθ = 26.8 isopycnal (approximately the upper 300 m of the water column) in the North Brazil Current (NBC) retroflection region (0° to 14°N, 60° to 40°W) during August of 1989. The water column is divided into a near-surface, upper thermocline layer (above σθ = 24.5) and a main to subthermocline layer (σθ = 24.5 to σ0 = 26.8). In the upper layer the eastward flowing North Equatorial Countercurrent (NECC) is composed of 16×106 m3/s of NBC transport that has retroflected from the coast between 6°N and 8°N and 8×106 m3/s of North Equatorial Current (NEC) transport returning eastward. An anticyclonic eddy with a 10×106 m3/s transport lies northwest of the NBC retroflection. No throughflow is observed along the boundary, and only a small portion of the observed NEC transport (1.5×106 m3/s) enters the Caribbean Sea. In the lower layer the NBC transports 8×106 m3/s into the subthermocline North Equatorial Undercurrent (NEUC). In addition, 15×106 m3/s joins the NEUC from the north. At 44°W the subsurface core of the NEUC lies south of the near-surface core of the NECC. Nearly half of the NEUC transport is made up of a mixed water type with salinity-oxygen (S-O2) characteristics intermediate to the characteristics of the original component transports. There is no evidence of continuous NBC flow into the Caribbean Sea in the lower level. The closed eddy to the north of the retroflection, however, contains water masses with South Atlantic S-O2 properties.

Transition regions and their role in the relationship between sea surface height and subsurface temperature structure in the Atlantic Ocean

Expendable bathythermograph (XBT) profiles and TOPEX/Poseidon altimeter data (T/P) are compared for the years 1993 through 1997 to determine how much can be understood about water column variability from XBTs given only sea height anomalies (SHA) from T/P. Our focus is on the annual cycle along two well sampled XBT sections in the Atlantic Ocean from 10°S to 40°N. Regions of transition are identified that separate the mid-latitudes where surface buoyancy fluxes dominate the forcing of sea level, from those in the equatorial region where thermocline effects dominate. Zones of transition occur in the vicinity of troughs where small fluctuations in SHA belie the true nature of water column variability. Here, surface and thermocline variability tend to cancel each other. Thus, the character of SHA in transition regions emphasizes how important direct observations can be in interpreting satellite altimetric observations correctly when both surface and thermocline variability are important but are compensating in nature.

Deep flow along the western boundary south of the Blake Bahama Outer Ridge

Abstract In June–July 1990, hydrographic, chlorofluorocarbon (CFC), and velocity observations were taken along the western boundary of the North Atlantic south of the Blake Bahama Outer Ridge from 30° to 24°N between the northern Bahamas and 71°W. The deep flow in the region, associated with the deep western boundary current, forms a pattern of strong, narrow currents and cyclonic gyres close to the continental slope with broad, slower southward flow offshore. The CFCs reveal that the most recently “ventilated” water (i.e., having the highest CFC concentrations due to more recent contact with the atmosphere in the northern North Atlantic) is found along the western boundary in two distinct cores between potential temperatures 4°–6°C and 1.9°–2.4°C. Geostrophic transport streamlines were constructed for the deep flow, referenced using direct velocity observations at 26.5°N and assuming mass conservation between closed areas bounded by the hydrographic sections. The tracers and transports are used together ...

Current variability and its relation to sea‐surface topography in the Caribbean Sea and Gulf of Mexico

The circulation in the Caribbean Sea and Gulf of Mexico exhibits considerable variability, which manifests itself in the form of changes in the intensity and location of the major currents. These changes in current intensity and location are coupled with changes in the distribution of the sea‐surface topography. Little is known of the temporal and spatial distribution of currents in the eastern Caribbean Sea. Recent direct measurements suggest a complicated current structure with large meanders and eddies; such a structure implies a complicated sea‐surface topography. An anticyclonic gyre, characterized by a rise in the sea‐surface topography, is frequently found in the western Caribbean Sea. The gyre is bounded on the south and west by intense currents. Sea‐surface slopes of 0.4m/200km have been observed across the southern limb of the gyre, the Cayman Current, and 0.5m/100km across the western limb, the Yucatan Current. There appears to be a seasonal cycle in the intensity of this gyre, which implies se...

The Relationship of the Curl of the Local Wind Stress to the Circulation of the Cayman Sea and the Gulf of Mexico

Abstract The curl of the annual mean wind stress is proposed as the forcing mechanism for the anticyclonic gyre observed in the Cayman Sea. A simple wind-driven model is presented to illustrate how a steady-state gyre in the Cayman Sea and another gyre in the western Gulf of Mexico can be spun-up by the wind. The model results also indicate that the exchange of mass between the two basins can be enhanced by the wind field. Temporal changes in the upper layer temperature structure of the Cayman Sea gyre are consistent, qualitatively, with changes predicted by a simple wind-forcing model. The same model does not appear valid in the western Gulf of Mexico.

Near Surface Temperature Observations Obtained in the Equatorial Atlantic Ocean During Fgge (1979)

Temperature and surface wind data collected across the equatorial Atlantic Ocean during the First GARP Global Experiment (FGGE), 1979, have been compiled to study the seasonal evolution of the near-surface temperature field. The development of the large-scale, sea-surface temperature (SST) field is characterized by the appearance during boreal summer of a tongue of cold water which extends from the eastern to western basin, on and south of the equator. During 1979, the cold water first appears at 4°W and 28°W during early May and at 22°W some four weeks later. East of about 20°W, the thermocline rises and the mixed layer becomes shallower simultaneously with the lowering of SSTs. West of about 30°W, the thermocline and mixed layer deepen at this time. Below average temperatures are observed through October, as the thermocline redeepens in the east and continues to deepen in the west. The 1979 SST and thermocline distributions along the equator have been compared to climatological distributions derived from historical data. The FGGE year fields are qualitatively similar to the climatological fields. Surface wind data collected during FGGE indicate that the surface cooling occurs within several days of an increase in both components of wind at 4°W and 28°W and within several weeks of the wind increase at 22°W.

The Atlantic Climate Change Program

The Atlantic Climate Change Program (ACCP) is a component of NOAAs Climate and Global Change Program. ACCP is directed at determining the role of the thermohaline circulation of the Atlantic Ocean on global atmospheric climate. Efforts and progress in four ACCP elements are described. Advances include (1) descriptions of decadal and longer-term variability in the coupled ocean-atmosphere-ice system of the North Atlantic; (2) development of tools needed to perform long-term model runs of coupled simulations of North Atlantic air-sea interaction; (3) definition of mean and time-dependent characteristics of the thermohaline circulation; and (4) development of monitoring strategies for various elements of the thermohaline circulation. 20 refs., 4 figs., 1 tab.

The Formation of the Yucatan Current Based on Observations of Summer 1971

Abstract Temperature, salinity and Lagrangian current data collected during the summer of 1971 in the western Caribbean Sea are employed to evaluate the ageostrophic components of the flow in the formation region of the Yucatan Current. The ratio of tangential and centripetal accelerations to Coriolis acceleration for data averaged over 24 h periods remain less than 10% except in two areas. An anticyclonic turn, centered at 19°30′N, 86°W, has the largest centripetal accelerations, and in the region of Cozumel Island significant tangential accelerations occur. The large-scale accelerations and additional evidence support the hypothesis that inertial effects dominate in the formation of the Yucatan Current.

Lessons Learned From Operating Global Ocean Observing Networks

Abstract The Global Ocean Observing System Center (GOOSC) at the National Oceanic and Atmospheric Administrations (NOAA) Atlantic Oceanographic and Meteorological Laboratory operates two global observing networks, a drifting buoy array, and a Voluntary Observing Ship network. The arrays provide in real time surface atmospheric and subsurface oceanographic data needed by NOAA weather and climate forecasters. The data are used in delayed mode to verify model simulations of the ocean and atmosphere, to provide in situ calibration/validation data for remote sensing observations, and to increase understanding of the dynamics of the ocean and atmosphere. The operational and research lessons learned in the operation of the GOOSC are reviewed. Operationally, it was learned that, because of costs, international participation is required to maintain global networks; data management methodology is a critical component of operations; and integrated observing systems using multiple platforms provide more accurate pro...