摘要:

A remote optical settling tube was deployed in the deep ocean to obtain the first ever in situ distributions of particle settling velocity. These distributions were extrapolated to particle size distributions assuming several possible fixed and variable (with size) particle densities. Cumulative slopes of the particle size distribution (with fixed particle densities of 1.1–2.0 g cm−3) were consistent with earlier measurements made shipboard in the same region. Cumulative slopes obtained using a more realistic variable density (as would be the case for populations including zero‐order and first‐order aggregates) were considerably lower, suggesting that the remote settling tube is detecting aggregated material more accurately than can be done with impedance‐based particle size analyzers. This is supported by the fact that the particulate relative real refractive index was also computed from the specific beam attenuation coefficient and yielded expected results only when the variable density size distribution was applied. These data and analyses demonstrate that the remote optical settling tube can be used effectively (even at low concentrations of suspended material) for in situ determinations of the particle size distribution, especially where relatively fragile aggregates may b

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00931

年代:1989

数据来源: WILEY

摘要:

We analyze spectra from five sets of hourly vertical profiles of upper‐ocean horizontal velocity collected with the Cartesian Diver velocity recorder. Each set consists of 11 to 27 profiles over depth ranges of 25–220 m to 25–340 m. The vertical wave number (m) power spectra of velocity and shear have no reproducible power law form in the band [0.02–0.1] cpm. Shear spectra tend to rise then fall with increasing wave number, with the transition wave numbermcvarying within the above band. For shear spectra, steepness atmnear 0.1 cpm ranges fromm−1/2tom−2. The data sets fall into two categories. For one group, inverse Richardson functionsRi−1(mc) have values near 2. Despite variability of velocity variance, these sets haveRi−1(0.1 cpm) ≈ 3, suggesting that shear is near saturation. Low variability ofRi−1(0.l), despite high kinetic energy variability for this group, suggests that energy at high wave number (and thus shear) is suppressed. This suggests that instability mechanisms attenuate spectra at high wave number, with attenuation becoming more broadband and influencing progressively lower vertical wave numbers (in addition to consistently influenced high wave numbers) at higher energy. For the other group,Ri−1(0.1) ≈ 1, shear spectra are less steep, and shear is concentrated at high wave number, suggesting less attenuation at the small‐scale end of our measurement band. For both groups, predicted wave numbers of spectral steepening, estimated from the data using two techniques, are related approximately inversely with horizontal kinetic energy in the band [0.005–0.01] cpm, quantifying

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00939

年代:1989

数据来源: WILEY

摘要:

The numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches. The numerical model is one‐dimensional in the cross‐shore direction and is based on the finite amplitude, shallow water equations, including the effect of bottom friction, which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint. The slight modification is related to the effect of the time‐averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes. The modified numerical model is compared with available small‐scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope. Additional comparisons are made with small‐scale tests conducted using transient monochromatic and grouped waves on a 1:8 smooth slope with and without an idealized nearshore bar at the toe of the 1:8 slope. As a whole, the numerical model is shown to be capable of predicting both time‐varying and time‐averaged hydrodynamic quantities in the surf and swash zones on gentle as well as

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00951

年代:1989

数据来源: WILEY

摘要:

The effect of wave breaking on the probability function of surface elevation is examined. The surface elevation limited by wave breaking ζb(t) is first related to the original wave elevation ζ(t) and its second derivative ¨ζ(t). An approximate, second‐order, nonlinear, non‐Gaussian model for ζ(t) of arbitrary but moderate bandwidth is presented, and an expression for the probability density function ƒb( ) of ζb(t) is derived. The results show clearly that the effect of wave breaking on the probability density function of surface elevation is to introduce a secondary hump on the positive side of the probability density function, a phenomenon also observed in wind wave tank e

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00967

年代:1989

数据来源: WILEY

摘要:

In the next decade a wealth of ocean surface data will become available through the launch of satellites such as ERS 1. We discuss the problem of how to make optimal use of this data. We have investigated the benefits of having a coupled wind‐wave analysis over the oceans for quality assessment of satellite data, for monitoring the performance of the algorithms (e.g., for the scatterometer), and for producing consistent wind and wave analyses. Using a reliable wave prediction scheme, the WAM model, we show how to cross validate altimeter wave height with scatterometer data and how to construct an analyzed wave model spectrum from the altimeter wave height. The analyzed wave spectrum may be cross validated with the synthetic aperture radar image spectrum. Implications for improvement of, for example, the Seasat scatterometer algorithm are pointed ou

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00973

年代:1989

数据来源: WILEY

摘要:

A technique is presented to remotely measure the scales and morphology of natural sand bars based on the preferential dissipation of wind waves and swell over the crests of the bar. Photographic or video images are recorded and statistical uncertainties associated with incident wave height modulations removed by averaging (time exposures). Ground truth testing of the technique was carried out as part of the SUPERDUCK experiment in October 1986. The time exposures generally provided a good mapping of underlying morphology, allowing detection of the bar and determination of cross‐shore and longshore length scales. However, during high waves, persistent surface foam obscures the relationship of image intensity to local dissipation (modeled theoretically by dissipation of a random wave field), and an enhancement technique of image differencing must be done to remove the bias. Errors in the estimate of bar crest distance from the shoreline are generally less than 35%, but this value depends on the geometry of the particular bar. Logistic simplicity and quantitative capabilities make this technique very attractiv

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00995

年代:1989

数据来源: WILEY

摘要:

Assuming linear wave theory for waves riding on a weak current of 0(ε) compared to the wave phase speed, an approximate dispersion relation is developed to 0(ε2) for arbitrary current U(z) in water of finite depth. The 0(ε2) approximation is shown to be a significant improvement over the 0(ε) result, in comparison with numerical and analytic results for the full problem. Various current profiles in the full range of water depths are considered. Comments on approximate action conservation and application to depth‐averaged wave models are inc

ISSN:0148-0227    

DOI:10.1029/JC094iC01p01013

年代:1989

数据来源: WILEY

摘要:

Barometric pressure and total ozone content may significantly depart from their mean climatology values; these values, however, are used when processing the visible remote sensing (VRS) data with the aim of estimating the phytoplanktonic pigments concentration (chlorophylla+ phaeophytina, in milligrams per cubic meter) within the upper ocean. The effect of ignoring such departures upon the retrieved concentration has been simulated for the broad oceanic range (0.015–20 mg/m3). The simulation is effected for typical VRS situations (geometry, aerosol) when information about the variable aerosol is not available when entering the processing (as is the case with the Coastal Zone Color Scanner (CZCS) data) or, conversely, when such information has been separately obtained (simulation of future sensors with dedicated near‐IR channels). The result is that in both these cases the use of mean climatology values leads to variable misestimates of the pigment content, by a factor of up to 2 in many common VRS situations, and above 2 for very low or high actual pigment content. After the results are discussed, the conclusion is that the actual values of the barometric pressure and of the ozone content will have to be introduced in the processing of future visible sensor data in order to preserve the expected accuracy. With regard to the exploitation of the CZCS archive, this requirement is not so essential, insofar as the pressure and ozone effects on the pigment concentration retrieval remain of the same order as the noise due to the limited radiometric accuracy of this sensor. However, at the scale of a CZCS scene, neglecting the strong structures in the pressure and ozone content fields may bias the phytoplankton concentration mapping. The use of the actual values is therefore recommen

ISSN:0148-0227    

DOI:10.1029/JC094iC01p01029

年代:1989

数据来源: WILEY

摘要:

Atmospheric deposition contributes copper to the surface ocean. The biogeochemical importance and fate of this copper is poorly understood for open ocean regions. Atmospheric aerosols collected at Enewetak Atoll, in the tropical North Pacific, were exposed to seawater and artificial rainwater in laboratory experiments. Aerosol copper during the high‐dust season at Enewetak Atoll is made up of aluminosilicate, oceanic, and possibly soil organic matter components. During the low‐dust season, aerosol copper appears to be essentially all of oceanic origin. Virtually all nonaluminosilicate copper in marine aerosols collected at Enewetak is soluble in seawater. Dissolved organic matter and possibly cations in seawater increase the dissolution of aerosol copper. The net atmospheric flux of soluble copper to the tropical North Pacific near Enewetak is approximately 0.13 nmol cm−2yr−1out of a total net atmospheric copper flux of 0.14 nmol cm−2yr−1. Atmospheric deposition supplies roughly the same quantity of soluble copper to tropical open North Pacific surface waters as does upwelling to eastern North Pacific surface waters. Atmospheric copper deposition, which appears to be primarily of natural origin, may be the most important input of copper to the surface waters of the central gyre of the No

ISSN:0148-0227    

DOI:10.1029/JC094iC01p01039

年代:1989

数据来源: WILEY