摘要:

The seasonal baroclinic circulation in the Gulf of Maine is partly determined by the distribution of dense water that enters from the continental slope and spreads over sills into the deep basins of the Gulf. The slope water enters the Gulf as an intermittent deep flow through the Northeast Channel, which provides the principal connection with the Atlantic Ocean. Warm‐core rings from the Gulf Stream occasionally approach the mouth of the Northeast Channel, and at times, ring water contributes to or modifies the inflowing slope water. For example, sequential surveys in June and July of 1986 showed that a ring streamer crowded against Georges Bank and brushed obliquely across the channel mouth. The resulting inflow in July flooded the channel mouth with streamer‐modified slope water, which overwhelmed the more usual Maine Intermediate Water outflow noted 1 month earlier. Compared to previous years, relatively little slope water was found inside the Gulf in June 1986, and it is tempting to speculate that a delayed spin‐up of the interior baroclinic circulation began with the major inflow episode observed in July. Warm‐core rings from the Gulf Stream may influence the timing, intensity, and structure of the circulation and dependent processes that develop each year in the Gulf of Maine. A test of this hypothesis will require long‐term monitoring of the Northeast Channel region, coupled with seasonal hydrographic surveys and current measurements at strategic locations inside the Gulf

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08183

年代:1987

数据来源: WILEY

摘要:

Moored measurements of the surface wind and of the current and temperature fields within the uppermost 250 m were recorded from March 1980 to September 1985 at 0°, 110°W and from July 1981 to November 1983 at 0°, 95°W. At these sites the annual mean thicknesses of the equatorial undercurrent (EUC) and of the surface portion of the south equatorial current (SEC) were about 200 m and 20 m, respectively. The annual mean EUC core speed was 0.9 m s−1. Annual cycles of temperature and zonal current at 110°W were most distinctive near the surface: at nominal depths of 15 m and 47.5 m, the average annual amplitudes were 1.5°C and 0.5 m s−1; at about 100 m the annual amplitudes were about 0.5°C and 0.10 m s−1. At 15 m the annual mean zonal current was 0.05 m s−1, which was not representative of the monthly mean zonal current; in April the monthly mean direction was eastward, and in October it was westward with speeds of about 0.5 m s−1in both months. Warmer water occurred in April and colder water in October. The direction of the zonal wind component was westward throughout the year, and the annual amplitude of the zonal wind was only about 2.5 times larger than that of the zonal current. The average amplitude of the annual cycle of the meridional current component was less than 0.05 m s−1and not distinguishable from year‐to‐year monthly mean variations. Monthly mean anomalous or El Niño currents at 110°W were defined as the difference between the observations and the annual cycle. During the August‐December 1982 onset phase of El Niño, the strength of the normally westward flowing near‐surface SEC was greatly reduced to near‐zero speed by an El Niño eastward flowing zonal current of about 0.3 m s−1. The largest vertically averaged (15–250 m) zonal current anomaly (≈−0.5 m s−1) occurred in January and February 1983 and represented a substantial decrease in the eastward transport of the EUC, causing a disappearance of the undercurrent. The duration of the EUC disappearance was longer at 95°W than at 110°W. A surface‐intensified, eastward jet with a maximum daily speed of 1.75 m s−1at 15 m occurred in May 1983 at 110°W but not at 95°W. A massive redistribution of heat throughout the mixed layer and thermocline was associated with the 1982–1983 El Niño. Beginning in August 1982, the thermocline at 110°W and 95°W sank 100 m, reaching its maximum depth in December 1982; temperatures at 100 m and 150 m, which normally were about 15°C and 14°C, reached 27.5°C and 22.5°C. The time rate of change of the 15‐ to 200‐m heat content was 500 W m−2during the August‐December 1982 warming phase and −460 W m−2during the January‐February 1983 subsurface cooling phase. The EUC disappeared during the subsurface cooling phase. A second, less inte

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08197

年代:1987

数据来源: WILEY

摘要:

A series of numerical experiments with a reduced‐gravity, quasi‐geostrophic model were performed to investigate the adjustment of vortices to large‐amplitude perturbations of azimuthal modes 2 and 3. The results indicate that for vortices with length scales near the radius of deformation, almost 100% of the azimuthal mode energy is transferred to the axisymmetric flow. The time scale is of the order of the circulation time scale but exhibits a strong dependence on the perturbation mode number. The β plane cases show that this strong axisymmetrization tendency is almost completely unaffected by variations in the Coriolis parameter. The energetics of the perturbed β plane cases are virtually indistinguishable from the energetics of the unperturbed cases after 2–3 circulation periods, except for the cases with the strongest perturbations. Vorticity plots reveal that in the most perturbed cases, excess vorticity in the ends of the ellipse is removed in the form of elongated streamers. In some regions of the parameter space, these streamers roll up into cyclone‐anticy

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08213

年代:1987

数据来源: WILEY

摘要:

The flow of marine atmospheric boundary layer (MABL) air across ocean‐surface temperature fronts subjects the MABL to an abrupt change in surface thermal forcing. The MABL responds to this variable forcing by a readjustment of both the MABL heat and moisture content as well as the MABL depth. This note addresses questions raised in recent publications in this journal with a rigorous theoretical analysis for the simplest case, an equilibrated MABL crossing a very abrupt front at right angles. The MABL's adjustment is found by a solution to the mixed‐layer budget of buoyancy and the entrainment closure based on turbulent energetics of the MABL. Since the solution is analytic, this simple case can be easily extended to circumstances of more realistic forcing. The solution discussed here establishes a firm theoretical basis for previous, partly heuristic and partly empirical, work; highlights weaknesses of that approach, and shows how simplistic engineering solutions to complex geophysical problems can be completely mislead

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08226

年代:1987

数据来源: WILEY

摘要:

Clouds of bubbles generated by breaking waves were detected with a vertically directed high‐frequency echo sounder mounted on a submarine. Bubble concentration was inferred from a simple model of the bubble size distribution. The vertical and horizontal distribution of clouds is discussed in terms of wave‐breaking processes, air‐sea temperature differences, and subsurface motions which are thought to modulate the bubble concentration. Mean vertical profiles of bubble concentration decreased roughly exponentially with depth, withe‐folding depths between 0.7 m and 1.5 m. The mean bubble concentration at the surface,N–0, was found to increase with the wind speed measured at 10 m above the surface,U10, as. Various upper ocean dynamical processes are discussed in terms of their effects on the shapes and spacing of bubble plumes. The observations provide only weak evidence to support relationships between plume spacing and surface wave‐breaking events and between plume spacing and the expected scale of Langmuir

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08231

年代:1987

数据来源: WILEY

摘要:

A simple model for the near‐bottom combined wave and current flow over a moveable sediment bed is presented. The model is an extension of the Grant and Madsen (1979) combined wave and current model, with moveable bed effects on the physical bottom roughness included as by Grant and Madsen (1982). The unsteady conservation of fluid momentum and sediment mass equations, which are coupled through an eddy diffusivity closure scheme, are solved for the wave and current velocity profiles, along with the suspended sediment concentration and transport profiles. Sample runs are presented to illustrate the effect of varying wave conditions on the current, the mean sediment concentration, and the mean sediment transport. Results show that for fine to medium sands, self‐stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave‐current interaction. The theory easily can be generalized for inclusion in a full Ekman layer

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08244

年代:1987

数据来源: WILEY

摘要:

Markedly different scenarios have been proposed for the circulation of the Levantine Intermediate Water (LIW) in the southern part of the western Mediterranean Sea. Discrepancies result from the fact that large temperature and salinity values, which characterize LIW, are encountered both in the vicinity of Sardinia and off Algeria. Thus it was assumed that the circulation of LIW was divided into two major branches, one northward along the Sardinian continental slope and the other across the Algerian basin. Being dissatisfied with such a branch image of the circulation, we have put forth hypotheses (Millot, 1985, 1987) which now appear to be supported by the results of the Médiprod 5 experiment conducted in June 1986. We propose a scheme for the circulation of LIW in the Algerian Basin wherein a gravity flow is constrained by the topography around Sardinia and is subjected to sporadic spreading toward the open basin due to erosion of this vein by mesoscale eddies. Therefore it seems admissible that no branch of LIW flows off the Algerian coast

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08265

年代:1987

数据来源: WILEY

摘要:

Mean velocity and turbulence measurements are described for turbulent flows above laboratory water waves, under various wind and thermal stratification conditions. Experimental results, when presented in the framework of Monin‐Obukhov similarity theory, support local scaling based on evaluation of stratification effects at the same nondimensional distance (z+=zu*/ν) (definitions of the various symbols follow in section 2) from the mean water surface. Such scaling allows an extension of application of the above theory to the outer region of the boundary layer. Throughout the fully turbulent region, ratios of mean velocity gradients, eddy viscosities, and turbulence intensities under nonneutral and neutral conditions correlate well with the parameterz/Λ (Λ being a local Obukhov length) and show good agreement with established field correlations. The influence of stratification on the wind‐stress coefficient can be estimated from an empirical relationship in terms of its value under neutral conditions and a bulk Richardson

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08277

年代:1987

数据来源: WILEY

摘要:

Chemical mass balance models of river solution chemistry, constrained by geologic data and thermodynamic models, provide a consistent description of the weathering processes that occur in the Amazon Basin. In areas with high weathering rates, such as the Andes, calcium, magnesium, sulfate, and alkalinity come from the weathering of evaporite minerals, sulfides, and carbonates. The inputs of calcium, magnesium, and alkalinity from exclusively carbonate terrains are limited by calcite, and perhaps by dolomite, saturation. When evaporites are present, only the alkalinity inputs are so limited because of additional weathering sources of calcium and magnesium. Dissolved silica, potassium, and sodium can be used to define mass balance relationships that in turn establish the nature of the clay mineral suites which are consistent with solute compositions. Use of thermodynamic constraints, specifically kaolinite and quartz stability, assists in data interpretation. At lowest weathering rates, all common primary minerals exposed to weathering are broken down to release silica and cations; quartz, kaolinite and (Fe,Al)‐sesquioxides all appear to be unstable. At higher weathering rates, enough silica is available to stabilize kaolinite, then quartz. The stabilization of Si‐bearing phases is reflected by a drop in the ratio of silica to other dissolved components. Finally, at the highest weathering rates, such as in the Andean catchments, high cation levels result in the formation of the 2:1 clays, which sequester even more silica, and any clear relationship between silica and other solutes degenera

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08293

年代:1987

数据来源: WILEY

摘要:

Wind measurements at 3.8 m from a surface‐following toroid and at 4.0 m from a vertically stable spar were compared to estimate the influence of mooring motion. Buoys were separated by 9 km. Data were obtained at 15‐min intervals for 41 days in the equatorial Pacific, where the maximum 15‐min averaged wind speed was 9.0 m s−1and wind speeds averaged 4.5 m s−1. Toroid wind speeds were 3.5% greater than the spar data, and the correlation coefficient between 15‐min toroid and spar data was 0.92. The frequency of the 50% noise level was 0.125 cph, and the correlation coefficient between 8‐hour averaged toroid and spar data was 0.98. Toroid 8‐hour averaged wind speeds referenced to 10‐m height were 2% larger than corres

ISSN:0148-0227    

DOI:10.1029/JC092iC08p08303

年代:1987

数据来源: WILEY