摘要:

A linear numerical model forced by winds estimated from ships for each month from January 1961, to December 1970, is used to study the interannual variability of the equatorial Pacific. Model pycnocline variability at the Galapagos Islands is very similar to the observed variability of sea level. The maximum significant cross correlation of the two records is near zero lag. The 1963, 1965, and 1969 El Niño events are characterized by a persistently deep pycnocline. The model pycnocline variability at Talara, Peru, leads the observed SST variability by 2 months. The lag structure of pycnocline variability cross correlations indicates that the variability at the equator is related to the excitation of internal Kelvin and Rossby waves. The onset of the 1965 and 1969 El Niño events was triggered by a large amplitude downwelling Kelvin wave excited by relaxation of the easterlies west of the dateline. None of the El Niño events of the 1960's were related to anomalous relaxations of the wind field over the central Pacific. In addition, the seasonal intensification of the southeast trades over the central Pacific was not as strong as during non‐El Niño years. The subsequent cessation of the remotely forced seasonal upwelling caused the pycnoline to be depressed throughout the El Niño year. During the southern summer, reestablishment of the semiannual variability of the southeast trades over the central equatorial Pacific excited a seasonal downwelling Kelvin wave. This second major downwelling impulse resulted in the double peak downwelling signature observed in sea level records. The minor El Niño of 1963 was soley due to the cessation of the semi‐annual wind stress variability east of 180°. The absence of remotely forced upwelling Kelvin waves kept the pycnocline deeper than normal following the seasonal downwelling at the outset of the year. There was not a relaxation of the wind field west of the dateline prior to the 19

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10901

年代:1981

数据来源: WILEY

摘要:

Three days of simultaneous near‐surface current measurements made by Coastal Ocean Dynamics Applications Radar (CODAR) and surface‐moored Vector‐Averaging Current Meters (VACM) in the Strait of Juan de Fuca are compared. The study focuses on the mean flow and tidal components that contained approximately 79% of the kinetic energy. The mean speed and direction differences were less than 7 cm/s and 10°, respectively. TheK1andM2tidal constituents agreed to within 14 cm/s with a mean difference of 5.2 cm/s. This study demonstrates that CODAR yields estimates of the near‐surface currents that are comparable with conventional VACM arrays to 10

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10908

年代:1981

数据来源: WILEY

摘要:

The effects of islands on equatorially trapped waves induced by the sudden onset of zonal wind are investigated by solving the shallow water equations numerically. The energy propagation associated with an equatorial Kelvin wave is almost unaffected by an island on the equator. The energy transmission ratio is over 0.8 even when the north‐south extent of the island is the same as the Rossby deformation radius. It is also shown that the Maldive Islands in the Indian Ocean and the Gilbert Islands in the Pacific Ocean do not affect the energy flux associated with Kelvin waves significantly. The sea level near the island, however, differs significantly from the sea level associated with an equatorial Kelvin wave in the absence of an island. This result has important implications for the interpretation of sea level measurements at equatorial islands. On the other hand, the energy propagation of equatorial Rossby waves (the lowest mode in the north‐south direction) is greatly affected by an island on the equator. The energy transmission ratio is less than 0.3 when the north‐south extent of the island is the same as the radius of deform

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10913

年代:1981

数据来源: WILEY

摘要:

This paper describes new methods for the interpretation of microwave scatter from the sea. Roughsurface scattering theory has led to an integral equation for the echo voltage in terms of the joint heightslope probability density function (pdf). We have developed methods for the inversion of this equation that do not require the assumption of a model for either the ocean surface or the transmitted pulse. In addition they are far more efficient than traditional grid‐search methods for model fitting. We have applied our methods to SEASAT data taken over Hurricane Fico. Statistical data analysis was performed to give the data covariance matrix and the correlation coefficient between successive waveforms and to trace the propagation of error through the inversion process to give statistical uncertainties in the derived parameters. The usual assumption of Rayleigh statistics is shown to be violated by the data, since the number of degrees of freedom increases linearly with power, independent of sea state; we conclude that this is an instrumental effect. We find that the waveforms are significantly correlated over distances of several kilometers at high sea states and suggest coherence of long ocean waves over these distances as the cause. We obtained waveheight higher‐order parameters by least squares fitting of a Gram‐Charlier model for probability densities to the calculated values. For averages over 160 km of sea, we obtain a mean surface height bias correction, significant waveheight, and height skewness parameter with standard deviations of 4, 0.7, and 15%. In addition to this height bias correction easily removed from the data, we identify another sea‐state‐dependent height bias that can exceed 50 cm. That this exists in the data is proof that one must employ the joint height‐slope pdf in the scattering model, and not merely the height pdf as conventi

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10921

年代:1981

数据来源: WILEY

摘要:

The Geos‐3 satellite altimeter observed numerous sea surface profiles along nearly repeated tracks in the western North Atlantic during its 3.5‐year lifetime, enabling observation of the variation of sea surface topography along these tracks. Analysis of 14 north‐going and 13 south‐going sets of repeated tracks has yielded the variability of the surface at a resolution of 1° from 25° to 41°N latitude and from 60° to 80°W longitude. The observed rms variation of surface topography ranges from about 8 cm in the Sargasso Sea to a maximum of 48 cm in the Gulf Stream meander region, in agreement with known mesoscale energetics of

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10931

年代:1981

数据来源: WILEY

摘要:

Bagnold's energetics‐based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed. In both the bedload and suspended load, the transport rate vectors are found to be composed of a velocity‐induced component directed parallel to the instantaneous velocity vector and a gravity‐induced component directed down slope. The model is applied to idealized surfzone conditions, leading to estimates of the local longshore and onshore‐offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions. The model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions. The results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characte

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10938

年代:1981

数据来源: WILEY

摘要:

Measurements of tidal and wave water velocities which were made in shallow water near the seafloor in the Strait of Juan de Fuca indicate strong tidal current influence on waves. This effect is reflected in the variation of the velocity frequency spectrum with the direction and magnitude of the tidal current. The area under the spectrum decreases when the current propagates in the direction of the waves, and it increases when the current propagates against the waves. These spectral area variations increase with the current magnitude. The observations are generally consistent with predictions of a spectral model derived from the energy balance principle.

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10955

年代:1981

数据来源: WILEY

摘要:

A wind wave forecasting model is described, based upon the ray technique, which is specifically designed for shallow water areas. The model explicitly includes wave generation, refraction, and shoaling, while nonlinear dissipative processes (breaking and bottom friction) are introduced through a suitable parametrization. The forecast is provided at a specified time and target position, in terms of a directional spectrum, from which the one‐dimensional spectrum and the significant wave height are derived. The model has been used to hindcast storms both in shallow water (Northern Adriatic Sea) and in deep water conditions (Tyrrhenian Sea). The results have been compared with local measurements, and the rms error for the significant wave height is between 10 and 20%. A major problem has been found in the correct evaluation of the wind fiel

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10961

年代:1981

数据来源: WILEY

摘要:

An experiment to measure the dispersion of a passive tracer injected at 300 and 1000 m depth in the Pacific 600 miles southwest of San Diego is described. Rhodamine dye was released as a (very nearly). point source, and the subsequent growth of the patch was mapped at various times, up to 66.2 hours after release, using a self‐propelled underwater research vehicle (SPURV), which carried temperature, conductivity, pressure, and dye sensors on a depth cycling trajectory through the patch. The analysis shows that the horizontal diffusion rates decrease with depth, that it is difficult to resolve the mixing in terms of a constant diffusion parameter based on any one of a number of models, that the 300 m results agree with those obtained by Schuert (1970), and that the patch growth began to develop eddy behavior at 66.2 hours when the rms second moment of the dye distribution was (r2)l/2= 210 m. For the purpose of predicting horizontal mixing, the results indicate that eddy diffusivities of 1150 and 360 cm2/s at 300 and 1000 m, respectively, are the best fit values for spatial scales<200 m horizontally. Although we have focused on horizontal (isopycnal) diffusion, a few aspects of the vertical (diapycnal) characteristics of the patch are also discusse

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10974

年代:1981

数据来源: WILEY

摘要:

Measurements of vertical displacement and horizontal velocity finestructure near the equator at 110°W in the eastern Pacific Ocean are reported. Profiles were scaled to a constant Brünt‐Väisälä frequency ocean (No= 1 cph) in accordance with a WKBJ approximation. A total of 57 CTD casts between 3°N and 3°S taken during five cruises in 1979 were analyzed. Results show an equatorial enhancement of vertical displacement variance for vertical wavelengths longer than 50 sdbar (stretched decibars). This enhancement is similar to that which has been reported at 125°W and 179°E. Differences between locations can be accounted for by the observed temporal variability at 110°W. Coherence between vertical displacement profiles separated in time by delays of 2 hour to 120 hour indicate that the high wave number structures were largely associated with time scales of 4 days and less. Meridionally, vertical structures longer than 300 sdbar were coherent within 50 km of the equator. We interpret this vertical displacement fine structure enhancement as high wave number equatorially trapped inertial‐gravity waves. The velocity fine structure measurements in July 1979 also indicate equatorially enhanced horizontal kinetic energy for vertical wave lengths longer than 100 sdbar. The velocity structures persisted over the 56 hour of measurement and appeared to have longer time scales than the vertical displacements. Meridional energy exceeded zonal energy; however, the two components were coherent. We interpret these velocity structures as inertial‐gravity waves which were produced off the equator and are propagating through the eq

ISSN:0148-0227    

DOI:10.1029/JC086iC11p10983

年代:1981

数据来源: WILEY