摘要:

Two rings, shed by the Loop Current in 1980 and 1982, were observed for several months by satellite‐tracked drifters to migrate across the Gulf of Mexico. The drifter path data have been inverted to obtain estimates of the paths of the centers of the two rings, ring shape, and the swirl velocities. Three drifters were deployed in the 1980 ring, and the analysis of that data set establishes the variability of the above kinematic estimates for one ring. A comparison of the analysis of data from both rings provides some idea on inter‐ring variability. Both rings impacted the Mexican continental slope at about 22.8°N, 95.5°W. After a brief adjustment period, both rings reestablished and maintained a vortex character for several months in the slope region while migrating slowly to the north. The paths of the centers of the two rings along the slope are virtually identical. The same analysis routine was applied to some simulated drifter data obtained from the Hurlburt and Thompson (1980) Gulf of Mexico primitive equation model. In the midgulf, the agreement between the observed rings and the simulated ring is good, although the former showed stronger interaction with the continental slope topography and/or circulation than was seen in the latter. Along the slope, the model ring kinematic characteristics were in extraordinary agreement with the observa

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01189

年代:1988

数据来源: WILEY

摘要:

Profiles of currents, density, and microstructure were obtained in the Pacific Ocean on and near the equator at 140°W in late 1984 as part of the Tropic Heat program. During a 4½‐day time series on the equator, the shear zone above the core of the undercurrent had very low mean Richardson numbers,Ri, between ¼ and ½. Average turbulent dissipation rates, ε, were high in this zone, ≈ 10−7W kg−1, and varied by a factor of 100 between minima in the early afternoon and maxima at night. The signal reached to 90 m, well into the stratified zone. Eddy coefficients,K, were low at highRi, and gradually increased asRidecreased, until they rose dramatically nearRi= ½. The observedK(Ri) relations are specific to time, location, and temporal and spatial resolutio

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01199

年代:1988

数据来源: WILEY

摘要:

Further study is done of Holloway and Gargett's (1987) suggestion that it is possible to distinguish salt‐fingering microstructure signals from those induced by turbulence by using the kurtosis (the relative flatness) of the scalar probability distribution. Support for their result comes from an examination of towed measurements of conductivity gradient fluctuations from turbulent and salt finger patches in the Sargasso Sea; however, when data are examined from presumably salt finger interfaces in the thermohaline staircase east of Barbados (the Caribbean Sheets and Layers Transects (C‐SALT) experimental region), data segments are found having both the suppressed kurtosis values expected of salt fingering and the high values associated with turbulence. It is concluded that either turbulence or some other chaotic process is competing with salt fingering in the C‐SALT data or that the kurtosis discriminant is not as useful as Holloway and Gargett su

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01219

年代:1988

数据来源: WILEY

摘要:

A formalism is presented for fitting dynamic forecast models to asynoptic data. Because of the importance of wind stress forcing in oceanic models and of the inadequacies of wind stress observations, the formalism allows an oceanic model to be fit to both Oceanographic and meteorological data. Within the context of this formalism the important question of whether an asynoptic data set contains sufficient information to determine the model state completely and unambiguously is discussed. Because the information travels along wave characteristics, it is clear that for the data to be sufficient to determine the model state, they must be distributed so that every feature of the flow is seen at some time or another. Such widespread coverage of the oceans requires a data collection system that relies heavily on satellites. The formalism is illustrated using a highly truncated model of the wind‐driven equatorial ocean and computational examples demonstrate how surface elevation and wind stress observations might be used to recover the model stat

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01227

年代:1988

数据来源: WILEY

摘要:

A convolution method is developed for computing the bottom stress in a vertically integrated hydrodynamic numerical model. By this means the bottom stress is no longer related to the depth mean current as in a “conventional” vertically integrated model, and an enhanced representation of the bottom stress is possible (an “enhanced” vertically integrated model). Consequently, the enhanced model can reproduce phase lags and differences in direction between bed stress and depth mean current, which cannot be taken into account in conventional vertically integrated models. A linear or quadratic frictional formulation can be used with the method. Idealized calculations of wind‐induced flow in a rectangular basin show that the bed stress computed by the convolution method is in excellent agreement with that derived using a full three‐dimensional model. However, significant differences in the bed stress between the three‐dimensional and conventional two‐dimensional model are evident. Also in this paper, a method is developed for extracting current profiles from vertically integrated models. Current profiles extracted from the enhanced two‐dimensional model, for a range of frictional effects, are found to be in good agreement with those computed using a full three

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01241

年代:1988

数据来源: WILEY

摘要:

A model for the climatological mean sea surface temperature (SST) of the tropical Pacific Ocean is developed. The upper ocean response is computed using a time dependent, linear, reduced gravity model, with the addition of a constant depth frictional surface layer. The full three‐dimensional temperature equation and a surface heat flux parameterization that requires specification of only wind speed and total cloud cover are used to evaluate the SST. Specification of atmospheric parameters, such as air temperature and humidity, over which the ocean has direct influence is avoided. The model simulates the major features of the observed tropical Pacific SST. The seasonal evolution of these features is generally captured by the model. Analysis of the results demonstrates the control the ocean has over the surface heat flux from ocean to atmosphere and the crucial role that dynamics play in determining the mean SST in the equatorial Pacific. The sensitivity of the model to perturbations in the surface heat flux, cloud cover specification, diffusivity, and mixed layer depth is discusse

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01265

年代:1988

数据来源: WILEY

摘要:

A substantial part of the Norwegian Sea deep‐water outflow into the North Atlantic takes place via the Faroe Bank Channel, the deepest passage through the Greenland‐Scotland Ridge. In order to estimate this flux of cold, low‐saline bottom water, a field survey comprising hydrographie observations as well as current measurements was carried out in the channel during May 1983. Transport calculations were undertaken for a total of four sets of observations and yielded values ranging from 1.5 to 1.9 sverdrup. The outflow is most likely subjected to hydraulic control, and consequently, a simple model has been formulated in order to determine the maximum discharge through a rotating channel of parabolic cross section. This geometry is well‐adapted to the topography of the Faroe Bank Channel, and the theoretically predicted magnitude of the transport was found to be in good agreement with the obser

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01281

年代:1988

数据来源: WILEY

摘要:

A front‐tracking algorithm of Chern et al. (1986) is tested on the shallow‐water equations, using the Parrett and Cullen (1984) and Williams and Hori (1970) initial state, consisting of smooth finite amplitude waves depending on one space dimension alone. At high resolution the solution is almost indistinguishable from that obtained with the Glimm algorithm. The latter is known to converge to the true frontal solution, but is 20 times less efficient at the same resolution. The solutions obtained using the front‐tracking algorithm at 8 times coarser resolution are quite acceptable, indicating a very substantial gain in efficiency, which encourages application in realistic ocean models possessing two or three space dimen

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01293

年代:1988

数据来源: WILEY

摘要:

During February 1983, we carried out a field study in the Bering Sea on the nature of ice floe collisions and their relation to ice deformation. In the study we deployed on selected ice floes four radar‐tracked buoys, three of which contained triaxial accelerometers. These buoys were initially located in compact ice at a distance of about 100 km from the ice edge, with the separations between pairs of floes ranging from 300 m to 5 km. The buoys then drifted out toward the ice edge at a rate of about 0.5 km h−1, with the acceleration data being telemetered to an adjacent ship. The ice motion divided into two parts: an initial solid body translation with no relative buoy displacement, followed by a rapid transition to a period in which the buoy separations underwent large excursions. Examination of the accelerometer records shows two major collisions which were correlated with the large‐scale ice deformation and hundreds of small collisions which recurred at the ocean swell period. The first major collision occurred at the onset of ice deformation; the second occurred when two floes which had been diverging started to converge. The periodic collisions began following the major collisions; their magnitude depended on the local ice compactness and the size of the ocean swell ampl

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01303

年代:1988

数据来源: WILEY

摘要:

The entire set of Seasat A satellite Scatterometer (SASS) wind speed observations,Us, colocated with the buoy measurements of the wind speedUband wave heightH1/3is analyzed. The “error”Ub‐Usis found to be influenced by the degree of wind‐wave coupling. This coupling is quantified employing the ratio of the wave‐to‐wind energy densities:X∼ ρwg〈ζ2〉/ρaUb2. For the special case of a fetch‐limited wave growth,Xis shown to coincide with the wind fetch. It is found that when the coupling is weak, i.e., at largeX, the SASS tends to overestimate the wind speed, and vice versa. The magnitude of the trend is evaluated roughly as 0.5 m/s per 100 km ofX. The increased radar backscatter at largeXis explained by invoking the concept (due to V. Zakharov and his collaborators) of a Kolmogorov equilibrium range appearing in wave spectra of sufficiently developed seas when the wind input is concentrated at high frequencies. In this extreme case, the surface density of steep wavelet occurrence would be at its highest owing to a pronounced cascade pattern in the surface geometry. The fractal dimensionDHof such an idealized surface is estimated to be about 2.333. Further, it is suggested thatDHfor a general case is a function of sea maturity. Finally, it is concluded that both the probability and the surface density of steep wavelet events are increasing functions ofX. A major implication with respect to the electromagnetic scattering is that the so‐called spike component of the backscattering coefficient, formed from the individual radar returns caused by the steep and/or breaking wavelets, is controlled primarily by the large‐scale features of surface geometry, hence by such nonlocal factors of the wave dev

ISSN:0148-0227    

DOI:10.1029/JC093iC02p01317

年代:1988

数据来源: WILEY