摘要:

The Caribbean Sea is selected as a region where the large‐scale circulation is well determined by historical hydrographic measurements through application of the inverse method. A simple example is used to illustrate the technique and to demonstrate how some physically relevant quantities may be well determined in the formally underdetermined inverse problem. The geostrophic flow field in the Caribbean is found by imposing mass and salt conservation constraints in seven layers separated by surfaces of constant potential density. An unsmoothed solution is displayed that has weak dependence on an initial choice of reference level. In addition, a unique smoothed solution is shown. Above σθ= 27.4, the total flow leaving the western Caribbean is estimated to be 29 × 106m3s−1, in agreement with direct measurements. This flow is made up of 22 × 106m3s−1entering the Caribbean from the east and flowing across the southern half of the basin as the Caribbean Current, and 7 × 106m3s−1entering from the north through Windward Passage. Both of these currents show small‐scale variability that diminishes with distance from the respective passages. The deep flow has no net transport, as required by the shallow exit, but a well organized clockwise recirculation is found in the deep eas

ISSN:0148-0227    

DOI:10.1029/JC086iC09p07993

年代:1981

数据来源: WILEY

摘要:

Application of GOES archived data to determining sea surface temperature in the Gulf of Mexico is investigated for October 1977, a period when two research ships and three environmental buoys were available to provide surface calibration data. A theoretical error analysis is first used to explain the persistent differences between ship and operationally derived satellite temperatures and then is used to dictate a technique for applying full resolution archived GOES visible and infrared data to the problem. The technique developed first remaps the satellite scanline data into a rectangular matrix that covers the region of interest. Second, radiative transfer calculations are performed at each ‘cloud‐free’ station around the Gulf's periphery using LOWTRAN‐4. Third, least squares polynomial surfaces of atmospheric corrections are fitted to the perimetric radiative transfer results. Fourth, a bivariate Bayesian discriminant function, which uses cloud‐free areas as training sets, is used to classify objectively clear ocean radiance measurements. Fifth, the GOES is calibrated by comparing in situ measurements with calculated theoretical satellite temperatures. Sixth, maps of sea surface temperature are produced and compared with ship reports and a marine atlas. Root‐mean‐square calibration errors of GOES surface temperature determined by the above outlined approach was ±1.2 K when using all available surface reports and ±0.5 K when using only research ship, XBT, and environmental buoy reports. Evaluation of the infrared multispectral approach planned for NOAA‐C shows that for a mesoscale area the two techniques result in similar errors, and that ±1.0 K or slightly less is probably the geophysical

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08007

年代:1981

数据来源: WILEY

摘要:

The surface and near‐surface (30 m) currents of the eastern mid‐latitude Pacific obtained from 32 satellite‐tracked drifting buoys during the period June 1976 through August 1977 are discussed. These observations of oceanic currents are merged with and are compared to Fleet Numerical Weather Center's daily estimates of surface winds for the same period. Statistical comparisons of these data sets reveal that the drifters move systematically approximately 30° to the right of the surface wind at approximately 1.5% of the wind speed. This relationship between drifter movement and surface winds occurs during the entire period except for the summer months of 1976 when independent of the surface winds the buoy trajectories indicate mesoscale eddy motions with 100 km and 30 day time and space scales, respectively. Drifter liftimes exceeded that of the 9‐m diameter parachute drogues set at 30 m depth, thus enabling a comparison of the currents derived from the drifter motions at the surface and 30 m. These comparisons reveal no systematic difference in the drifter motions with and without drogues. These results suggest a rather uniform flow in the upper 30 m during periods of steady winds. The estimates of the nature of near‐surface currents obtained from the drifters differ from those predicted by Ekman's classical theory of wind‐driven flow, in that there is no evidence of either a reduction in speed or change in direction of the currents over th

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08022

年代:1981

数据来源: WILEY

摘要:

A pair of hydrographic sections (35°N, 155°W) were analyzed to compute absolute velocity by using a variation of the technique advanced by Stommel and Schott (1977). Absolute velocity is determined from an integrated form of the potential vorticity equation by a technique suggested by Davis (1978). This study is the first application of this technique that allows a direct comparison between the uncertainty in estimating a smooth density field and the amount of imbalance in the system of model equations. Because the amount of incompatibility (imbalance) in the system of equations is far smaller than is allowed by the uncertainty in defining the smooth field, the model equation is considered adequate for this set of data. Below 400 m, the nearly constant zonal isopycnal slope indicates that potential vorticity is uniform on isopycnal surfaces. Since the method depends on resolving flow directions from the intersection of isopycnals and surfaces of constant potential vorticity, the absolute velocity is indeterminate in this region. The model equation does, however, constrain the structure of the meridional density field and requires a poleward shift in the latitude at which successively deeper isopycnals reach their maximum depth. The fact that this poleward translation can be predicted over several degrees of latitude suggests potential vorticity is uniform over a substantial portion of the North Pacific subtropical gyre. This poleward translation of the density field is an aspect of subtropical density fields, in general, and occurs in conjunction with a translation in the field of geopotential anomaly. It is directly related to the curvature in the deep portion of the beta spira

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08031

年代:1981

数据来源: WILEY

摘要:

The structure of the near surface waters in the Southern Ocean, poleward of the Antarctic Polar Front but away from continental margins, is investigated with a three‐dimensional time‐dependent numerical model which resolves the annual sea ice cycle. The growth and decay of the ice field is predicted, using one of Semtner's (1976) thermodynamic ice models, in terms of specified atmospheric data and computed thermohaline characteristics of the ocean layers. The ice field is found to be sensitive to the lateral advection of heat by the oceanic circulation as well as vertical heat transports due to deep winter convection. The model treats the temperature minimum layer in the Southern Ocean as the remnant of a deep winter mixed layer which becomes capped by surface heating and precipitation in summer. The predicted thermohaline characteristics of the temperature minimum layer and the surface mixed layer are in good agreement with observations. Finally, the annual air‐sea heat exchange predicted by the model is discussed. The model's predicted area averaged heat loss experienced by the ocean south of the Atlantic Polar Front is much smaller than was previously estimated. This is attributed to errors in the southern region of the model domain. It is suggested that models, which include the interactions between sea ice and surface, deep and bottom waters along the continental margins, are needed to investigate this r

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08037

年代:1981

数据来源: WILEY

摘要:

Concentrations of copper, nickel, and cadmium have been determined for about 250 surface water samples. Nonupwelling open‐ocean concentrations of these metals are Cu, 0.5–1.4 nmol/kg; Ni, 1–2 nmol/kg; and Cd, less than 10 pmol/kg. In the equatorial Pacific upwelling zone, concentrations of Ni (3 nmol/kg) and Cd (80 pmol/kg) are higher than in the open ocean, but Cu (0.9 nmol/kg) is not significantly enriched. Metal concentrations are higher in cool, nutrient‐rich eastern boundary currents: Cu, 1.5 nmol/kg; Ni, 3.5 nmol/kg, and Cd, 30–50 pmol/kg. Copper is distinctly higher in the coastal waters of the Gulf of Panama (3–4 nmol/kg) and also higher in the shelf waters north of the Gulf Stream (2.5 nmol/kg); these copper enrichments may be caused by copper remobilized from mildly reducing shelf sediments and maintained by a coastal nutrient trap. In the open ocean, events of high‐Cu water (1.5–3.5 nmol/kg) are seen on scales up to 60 km; presumably, these are due to the advection of coastal water into the oceanic interior. The lowest copper concentrations in the North Pacific central gyre (0.5 nmol/kg; (Bruland, 1980)) are lower than in the Sargasso Sea (1.3 nmol/kg), while for nickel the lowest concentrations are 2 nmol/kg in both the North Pacific and the North Atlantic. Nickel and cadmium, while generally correlated with the nutrients in surface waters, show distinct regional changes in their element‐nutrient correlations. The residual concentrations of trace metals in the surface waters of the ocean can be explained if biological discrimination against trace metals relative to phosphorus increases as produ

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08048

年代:1981

数据来源: WILEY

摘要:

In an accelerating tidal flow the near‐bed velocity profile departs from the usual logarithmic form. The amount of the departure may not necessarily be large, but is nevertheless important when the profiles are used to calculate the bed roughness length and shear stress. A form for the accelerated profile is derived in terms of an ‘acceleration length’. Profiles measured off the SW coast of England are fitted to this expression, and give a value for a constant γ appearing in it. Published laboratory oscillatory flow profiles are also fitted; in this case the constant γ is larger due to the greater relative bed roughness. Von Karman's constant is obtained from the field data and found to be equal to 0.40, closer to laboratory values than to the now widely used atmospheric value of 0.35. Some evidence is found, however, to support a slow decrease in von Karman's constant with increasing boundary‐layer thickness to roughness len

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08067

年代:1981

数据来源: WILEY

摘要:

Wavestaff measurements made in the Gulf of Mexico and Waverider measurements from the Baltimore Canyon area have been used to study the form of ocean wave spectra at high frequencies. The observations are statistically consistent with the idea that the tail of the spectrum is in equilibrium with the local wind. Analysis showed that the spectral range between the mean wave frequency and about two and one half times that frequency is consistently proportional to the inverse of the fourth power of the frequency. At higher frequencies, the classical inverse fifth power law seems to hold. In the inverse fourth power range, the amplitude of the spectrum is also proportional to the wind friction velocity. These relationships should permit a reliable specification of this saturated range when only local wind observations are available. If the significant wave height and mean period are known, the amplitude of the tail of the spectrum can be predicted with somewhat greater accuracy. However, this relationship should be used with caution when the height and period statistics are influenced by swell.

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08075

年代:1981

数据来源: WILEY

摘要:

The relative contribution of jet and film drops from bursting bubbles to the sea‐salt component of the marine aerosol is poorly understood. An analysis of the bubble and aerosol spectra produced by a laboratory model of a breaking wave or whitecap shows that film drops may play a much more important role than previously accorded. The model strongly suggests that most of the droplets smaller than 5–10 μm in diameter originate as film drops, derived from bubbles larger than 1 mm. The water‐to‐air flux of such droplets is adequate to account for the majority of maritime cloud condensation nuclei. The model also suggests that droplets larger than 20–25 μm originate as jet drops, derived from bubbles smaller than 1 mm. The model breaking wave produces an upwelling plume of bubbles whose concentration for all bubble sizes vastly exceeds the steady state or background bubble population observed at sea at depths greater than 1 m. Bubbles of up to 10 mm diameter were produced, and the bubble flux reached 200 cm−2s−1. Whitecap bubble spectra, presently unavailable, are therefore essential in making more accurate assessments of marine aer

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08085

年代:1981

数据来源: WILEY

摘要:

A series of observing system simulation experiments has been performed to assess the potential impact of marine surface wind data on numerical weather prediction. Care was taken to duplicate the spatial coverage and error characteristics of conventional surface, radiosonde, ship, and aircraft reports. These observations, suitably degraded to account for instrument and sampling errors, were used in a conventional analysis‐forecast cycle. A series of five 72‐hour forecasts were then made by using the analyzed fields as initial conditions. The forecast error growth was found to be similar to that in operational numerical forecasts. Further experiments simulated the time‐continuous assimilation of remotely sensed marine surface wind or temperature sounding data in addition to the conventional data. The wind data were fabricated directly for model grid points intercepted by a Seasat‐1 scatterometer (SASS) swath and were placed in the lowest active level (945 mbar) of the model. The temperature sounding experiment assimilated error‐free data fabricated along actual Nimbus orbits. Forecasts were made from the resulting analysis fields, and the impact of the simulated satellite data was assessed by comparing these forecast errors with those of the control forecasts. When error‐free winds were assimilated by using a localized successive correction method (SCM), the impacts in extratropical regions proved to be substantial, especially in lower tropospheric quantities such as surface pressure. In contrast, a less sophisticated assimilation method resulted in negligible impact. The assimilation of error‐free sounder data (again by the SCM) gave impacts comparable to the wind data, suggesting that surface wind data alone may be as valuable as temperature soundings for numerical weather prediction. The effects of nominal SASS errors (±2 m/s in magnitude, ±20° in direction) on the impacts derived from wind data were f

ISSN:0148-0227    

DOI:10.1029/JC086iC09p08093

年代:1981

数据来源: WILEY