摘要:

A one‐dimensional ice‐ocean model consisting of a second moment, turbulent closure, mixed layer model and a three‐layer snow‐ice model has been applied to the simulation of Arctic ice mass and mixed layer properties. The results for the climatological seasonal cycle are discussed first and include the salt and heat balance in the upper ocean. The coupled model is then applied to the period 1880–1985, using the surface air temperature fluctuations from Hansen et al. (1983) and from Wigley et al. (1981). The analysis of the simulated large variations of the Arctic ice mass during this period (with similar changes in the mixed layer salinity) shows that the variability in the summer melt determines to a high degree the variability in the average ice thickness. The annual oceanic heat flux from the deep ocean and the maximum freezing rate and associated nearly constant minimum surface salinity flux did not vary significantly interannually. This also implies that the oceanic influence on the Arctic ice mass is minimal for the range of atmospheric variabili

ISSN:0148-0227    

DOI:10.1029/JC095iC09p15959

年代:1990

数据来源: WILEY

摘要:

This paper questions a recent claim (Gregg, 1989) that a first‐order understanding of the link between internal waves and turbulence has been achieved. It is demonstrated that (1) the theoretical basis of this result is extremely sensitive to an ad hoc assumption about the nature of the wavelength at which wave energy is delivered to dissipation (turbulence), (2) the method used by Gregg (1989) to calculate instantaneous wave field energy levelEis incorrect and will seriously underestimateEin cases whereEis greater thanEGM, the energy level of the GM (Garrett and Munk, 1975) canonical internal wave field, and (3) the range of variation ofEand buoyancy frequency N in the data sets reported by Gregg (1989) is not sufficient to rule out alternative scaling

ISSN:0148-0227    

DOI:10.1029/JC095iC09p15971

年代:1990

数据来源: WILEY

摘要:

The oceanic adjustment to variable winds in the presence of mean currents is studied by means of a shallow water model on an equatorialβplane. The waves that are available to affect the adjustment fall into two groups: a discrete, finite or infinite number of equatorially trapped modes, and a continuum of modes that are bounded by turning latitudes and/or critical latitudes. In response to variable winds, adjustment near the equator is very similar to the adjustment in the absence of the mean currents except for modifications to the speeds and structures of the waves that are involved. Off the equator, where the continuum of modes come into play critical layer absorption is a factor provided that the waves have a sufficiently large meridional group velocity to propagate to the critical layers in a reasonable time (before they cross the ocean basin, for example). Winds that are suddenly switched on excite waves with small zonal wave numbers and small meridional group velocities. The waves therefore succeed in effecting the adjustment. In the case of periodic winds, linear critical layer absorption modifies the shadow zones (Ekman response region) and regions of Sverdrup response that characterize the response in the absence of mean currents. In response to the annual harmonic of the wind the western part of the North Equatorial Countercurrent is unlikely to by affected by Rossby waves, because that is a shadow zone. The region between 10°N and 15°N approximately, the southern flank of the North Equatorial Current, is an interesting region because it is effectively a waveguide for modes with a turning latitude to the south and a critical latitude to the north. Wave trains are likely to be evident in that regi

ISSN:0148-0227    

DOI:10.1029/JC095iC09p15975

年代:1990

数据来源: WILEY

摘要:

The Subtropical Convergence Agulhas Retroflection Cruise, from February 12 to March 4, 1987, provided an opportunity for studying variability of surface heat fluxes and marine boundary layer modification within an ocean area where few atmospheric measurements have been made. From 3‐hourly surface observations it has been ascertained that surface heat flux processes are enhanced under cold air outbreak, postfrontal synoptic conditions and over warmer ocean areas. A maximum turbulent heat loss of 828 W/m2, 4 times the climatological value, was found. Over the cooler Subtropical Convergence waters and over the Agulhas Bank, heat fluxes were comparatively low. Two transect lines were performed across the Subtropical Convergence‐Agulhas SST front. In both cases, air temperatures, dew point temperatures, and particularly wind speeds increased over the warmer water owing to enhanced vertical mixing resulting from oceanic heat losses. The second transect revealed marked vertical shear of the zonal wind. The essential elements for cyclogenesis, namely, low static stability and strong low level baroclinicity, were found to be characteristic of the reg

ISSN:0148-0227    

DOI:10.1029/JC095iC09p15997

年代:1990

数据来源: WILEY

摘要:

A detailed hydrographic study of the East China Sea shelf edge north of Taiwan revealed an intense cold eddy on the shelf break and a large low‐salinity filament at the slope. The cold eddy which is induced by the upwelling of the subsurface Kuroshio water has been repeatedly documented in previous studies. The filament which is made of the mixed shelf and subsurface Kuroshio water, on the other hand, has not been recognized before. The shelf edge upwelling appears to be associated with the sharp bending of the Kuroshio north of Taiwan, while the outpouring of shelf water appears to be associated with the northeasterly storms. Both the eddy and the filament consist of large fractions of the subsurface Kuroshio water, and they may be important to the salt and nutrient budget on the East China Sea shel

ISSN:0148-0227    

DOI:10.1029/JC095iC09p16017

年代:1990

数据来源: WILEY

摘要:

The observed vertical nutrient distribution including a maximum at about 100 m depth in the Arctic Ocean is investigated using a one‐dimensional time‐dependent circulation model together with a simple biological model. The circulation model includes a shelf‐forced circulation. This is thought to take place in a box from which the outflow is specified regarding temperature and volume flux at different salinities. It has earlier been shown that the circulation model is able to reproduce the observed mean salinity and temperature stratification in the Arctic Ocean. Before introducing nutrients in the model a test is performed using the conservative tracer δ18(18O/16O ratio) as one extra state variable in order to verify the circulation model. It is shown that the field measurements can be simulated. The result is, however, rather sensitive to the tracer concentration in the Bering Strait inflow. The nutrients nitrate, phosphate, and silicate are then treated by coupling a simple biological model to the circulation model. The biological model describes some overall effects of production, sinking, and decomposition of organic matter. First a standard case of the biological model is presented. This is followed by some modified cases. It is shown that the observed nutrient distribution including the maximum can be generated. The available nutrient data from the Arctic Ocean are not sufficient to decide which among the cases is the most likely to occur. One case is, however, chosen as the best case. A nutrient budget and estimates of the magnitudes of the new production are presented for thi

ISSN:0148-0227    

DOI:10.1029/JC095iC09p16025

年代:1990

数据来源: WILEY

摘要:

Wave‐turbulence interaction may contribute to momentum and energy transfer in the near‐surface region beneath water waves. However, the nature and extent of this mechanism have not been well understood. A wave separation technique was developed to study quantitatively the momentum and energy transport due to wave‐turbulence interaction. In this technique a nonlinear stream function representation of the wave motion was determined so as to satisfy the kinematic and dynamic boundary conditions at the water surface. Wave‐induced velocities were then deduced from the stream function and subtracted from measured velocity components to obtain the turbulent flow field. This technique was applied to laboratory data taken beneath wind‐generated water waves. Coherence spectra indicate high correlation between turbulence and wave‐induced motions at some frequencies. Time‐averaged correlations between wave and turbulent velocities increase with wind speed and decrease with increasing distance away from the interface. Although there is no significant momentum transfer due to wave‐turbulence interaction, this mechanism results in significant energy transfer among the mean, wave‐induced, and turb

ISSN:0148-0227    

DOI:10.1029/JC095iC09p16037

年代:1990

数据来源: WILEY

摘要:

The predictions of linear and nonlinear (Boussinesq) shoaling wave models for nonbreaking unidirectional surface gravity waves are compared to field observations, with particular emphasis on quantities that may be important for cross‐shore sediment transport. The extensive data sets were obtained on two natural beaches, span water depths between 1 and 10 m, and include incident wave power spectra with narrow, broad, and bimodal shapes. Significant wave heights varied between approximately 30 and 100 cm, and peak periods between approximately 8 and 18 s. The evolution of total variances of sea surface elevation, cross‐shore velocity, and horizontal acceleration is modeled at least qualitatively well by both linear and nonlinear theories. Only the nonlinear theory predicts the increasingly asymmetric sea surface elevations and horizontal velocities (pitched‐forward wave shapes) and the weaker variation of skewness (difference between crest and trough profiles) which are observed to occur during shoaling. The nonlinear theory also models qualitatively well the large skewed accelerations which occur during the passage of asymmetric

ISSN:0148-0227    

DOI:10.1029/JC095iC09p16055

年代:1990

数据来源: WILEY

摘要:

In this work we test the compatibility between the theoretical parameters of a nonlinear wave model and the quantitative information that one can deduce from satellite‐derived data. The theoretical parameters are obtained by applying an inverse problem to the solution of the Cauchy problem for the Korteweg‐de Vries equation. Our results are applied to the case of internal wave patterns elaborated from two different satellite sensors at the south of Messina (the thematic mapper) and at the north of Messina (the synthetic aperture rad

ISSN:0148-0227    

DOI:10.1029/JC095iC09p16065

年代:1990

数据来源: WILEY

摘要:

Nearshore shear waves (also termed FIG or far infragravity waves) are investigated. Equations governing these motions, first observed by Oltman‐Shay et al. (1989) and modeled by Bowen and Holman (1989), are systematically derived using scaling arguments. The validity of these scalings is also verified, and a nondimensional parameter εTis identified as a possible measure of the intensity of the shear waves. This confirms the importance of the seaward facing longshore current shear, (or backshear), in determining the size and range of instability in the problem. The energy transfer between the mean flow (longshore current) and these oscillations is studied by deriving the energy equations. It is demonstrated that a necessary condition for the instabilities to grow is that the cross‐shore gradient of the horizontal Reynolds stress be nonzero. This suggests the possible importance of shear waves in nearshore mixing. This analysis is then applied to two simplified longshore current‐beach profiles; the first for constant depth (Bowen and Holman, 1989) and the second a more realistic sloping beach p

ISSN:0148-0227    

DOI:10.1029/JC095iC09p16075

年代:1990

数据来源: WILEY