摘要:

Oscillating wind with a periodPinduce variability with the following characteristics in the upper few hundred meters of the equatorial zone (5°N to 5°S) of the ocean. (1)P<10 days: these winds fluctuate too rapidly to generate strong currents and excite primarily waves. (2) 10 days

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01903

年代:1981

数据来源: WILEY

摘要:

Double diffusive convection is possible where large vertical gradients in temperature and salinity tend to compensate in density. Frontal intrusions have these large gradients and can provide the possibility for a salt finger interface at one boundary and a diffusive interface at the other. But large vertical gradients of velocity are present at the boundaries of intrusions, which cause mechanical stirring and turbulent mixing as well. In the exceptionally active intrusions at the Gulf Stream Front near 38°N 69°W, a convective process resulting from incomplete mechanical mixing was observed photographically on both intrusive boundarie

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01917

年代:1981

数据来源: WILEY

摘要:

The turbulent kinetic energy dissipation rate ε is estimated from measurements of small‐scale shear taken with a vertical profiler during the Fine and Microstructure Experiment (Fame). Typical profiles of ε are presented for the different oceanographic regions sampled, the Gulf Stream, a mid‐Sargasso site, and locations within and without the 1000 fathom (∼2000 m) contour about the island of Bermuda. Heavily averaged values of ε are presented as a function of mean Väisälä frequency, a fundamental scaling parameter for the oceanic internal wave field. A dependence ofis found for an ensemble of stations near Bermuda; functional dependence for an ensemble of stations at the mid‐Sargasso site is less clear, with results exhibiting an undesirable sensitivity to infrequent large events. Dissipation is found to increase as the island of Bermuda is approached from any direction: the density of measurements is insufficient to determine any azimuthal variation resulting from the anisotropic mean flow field about the island at the time. A set of three profiles across the Gulf Stream suggests that this is not a region of abnormally high dissipation, a conclusion supported by previous and concurrent measurements of temperature finestructure and m

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01929

年代:1981

数据来源: WILEY

摘要:

Thermal infrared data from the NOAA polar orbiting satellite and hydrographic observations from surface ships are used to estimate the eccentricity and the rotation rate of wavelike perturbations around the circumference of a Gulf Stream cyclonic eddy in April 1977. From the satellite data, the rotation rate is estimated at ω = (4.4 ± 0.1) × 10−6s−1for the period April 8–16. Estimates of ω are obtained from the trajectory of satellite‐tracked drifters and from changes in the sea surface temperature fields determined from expendable bathythermograph trace (XBT) surveys. A simple Eady model suggests the perturbations are stable modes of azimuthal wa

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01945

年代:1981

数据来源: WILEY

摘要:

Two deep arrays of current meters at heights of 1200 and 100 m above the bottom were set under the North Pacific Subtropical Gyre near 30°30'N, 157°45'W; the maximum record length obtained was 19 months. Autospectra show the following characteristics: strong peaks at the M2, S2 tidal frequencies; a broad peak at the diurnal‐inertial peak; a spectral gap centered at 0.02 c h−1; and a regular increase in energy with decreasing frequency below the gap. Rotary components tend to be counterclockwise below 10−2c h−1and clockwise above the diurnal‐inertial frequency. The M2 tidal amplitude ranged between 1.0 and 1.6 cm s−1; phase relationships suggest that a significant part of the motion is due to internal wave motion at this frequency. Low‐pass filtered velocity statistics show the following: evidence of nonstationarity in the variances between the first (9 month) and second (10 month) arrays; significant horizontal variation of mean kinetic energy on scales of 100 km; and time‐space averaged eddy kinetic energy is comparable in magnitude to the lowest values measured under the Subtropical Gyre in the western North Atlantic. Currents at 1200 m tended to be greater than at 100 m above the bottom. Spectra of the 100‐m records indicate the presence of two peaks at low frequency: a dominant and ubiquitous peak in the 1/105–1/175 c d−lfrequency band; and a secondary peak, which is shown in three of four moorings, in the 1/58–1/75 c d−1frequency band. Point estimates of the periods of the peaks give average values of 154 and 67 days. Comparison with subtropical western North Atlantic spectra shows that the ‘temporal mesoscale’ period (∼150 d) is somewhat higher in the Pacific data and it does not show the dominance of meridional motions observed in the Atlantic spectra. Plane wave fits to the 154‐day oscillation show the longest wave which closely fits the data has a wave length of 170 km and propagates toward 197°T. The westward phase propagation and particle orbits, which are transverse to the direction of propagation, are consistent with planetary Rossby wave dynamics. This wave does not fit the dispersion relation for flat‐bottom planetary waves; the observed phase speed is greater than that predicted by the dispersion relation. It is shown that either Doppler shifting of the frequency by the mean flow or topographic eff

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01955

年代:1981

数据来源: WILEY

摘要:

The response of the horizontal velocity field to forcing by the local wind was observed in the upper 150 m of the ocean by profiling with vector measuring current meters from the Research PlatformFlipas it drifted off the coast of California in January 1977. In the mixed layer, approximately 50 m deep, motion at frequencies lower than 0.1 cph was coherent with the wind stress. Rotary cross spectral analysis showed that the shear in the surface layer was related to the local wind stress and that the structure of the response at low frequencies was similar to but did not agree completely with the predictions of simple linear, eddy viscosity models.

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01969

年代:1981

数据来源: WILEY

摘要:

Relations have been developed for the entrainment of a turbulent layer into a stratified medium under the action of a surface stress. A constant gradient Richardson numberJis assumed at the interface, and the solutions are assumed to be self‐similar. It has been shown that the requirements of similarity are that the scales of the (mean and turbulent) velocity and temperature should all be powers of timet. The cases of linear and two‐layer density distributions have been given special attention, and a constant of proportionality in each case is determined by comparison with numerical solutions. The results are identical to those obtained by Pollard et al.‐type slab models ifRv≃ 2J, whereRv= buoyancy/(mean velocity)2. The nondimensional entrainment rate for the two‐layer case is nearly twice that for linear stratification, as observed. The density gradient in the two‐layer case is proportional tot−2, which explains the observed gradual disappearance of the density step. Numerical solutions show that the self‐similarity assumption is quite good with two layers and is approximately valid with linear stratification if 100

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01979

年代:1981

数据来源: WILEY

摘要:

A model of the planetary boundary layer flow over the Arctic pack ice was found to relate geostrophic flow determined from a large‐scale pressure field to the surface stress vector. A summary of the model and some data comparison is presente

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01989

年代:1981

数据来源: WILEY

摘要:

Green's Law for the propagation of a linear nondispersive wave in a gradually varying medium conserves energy, which is a quadratic integral property. Green's Law does not conserve linear integral properties, and other waves must arise. This paper treats some general properties that these additional waves must possess for a class that includes long linear water waves in a channel of gradually varying section. The major finding is that both a reflected wave and a re‐reflected tail are required to satisfy all of the conservation laws; integral properties of these additional waves are derive

ISSN:0148-0227    

DOI:10.1029/JC086iC03p01995

年代:1981

数据来源: WILEY

摘要:

A new method is presented for the depth interpolation of hydrographic data below the level of direct seasonal influence. It consists of interpolating (here, linearly) the departures of individual station data from a mean profile that has been estimated by cubic spline smoothing from an ensemble of stations occupied at the same or nearby locations. Repeated temperature profiles taken at thePanulirusstation off Bermuda are used for illustration. The rms interpolation error is estimated for a very large number of temperature measurements between 220 and 2000 m and compared to rms interpolation errors obtained with other methods. The new scheme performs best, particularly in data sparse regions. The interpolation method currently used at the National Oceanographic Data Center and the Aitken‐Lagrange interpolation yield a 30% larger rms interpolation error; the interpolation error for linear interpolation is more than 80% larger. The applicability of the interpolation method using the mean profile is also tested in the case where only a few stations are available to define the mean. Although the error reduction is smaller, the method still performs best when sets of four or more stations are availabl

ISSN:0148-0227    

DOI:10.1029/JC086iC03p02001

年代:1981

数据来源: WILEY