摘要:

A double inverse method to convert SAR data to estimates of current shear was developed theoretically. Problems of applying the technique to real SAR data were examined. The first step of the inversion process involved elimination of noise in the (x→, k→) wave spectra deduced from SAR images. The second step, estimation of current shear, required the existence of well defined swell and a favorable single of interaction between swell and ocean current. Application of the method in the Antarctic Circumpolar Current encountered sea conditions that both satisfied and violated these requirements. Where the wave‐current geometry was favorable, realistic surface current velocity fields were obtained, suggesting the presence of a substantial mesoscale eddy. Another attempt to apply the method in the Gulf Stream produced wave spectral estimates that showed no clear peak and hence produced no current es

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16087

年代:1989

数据来源: WILEY

摘要:

A numerical model is developed to study the thermodynamics of the Arabian Sea. The model consists of a surface mixed layer of thicknesshmand temperatureTm, embedded in a dynamic layer of thicknessh≥hm. Entrainment and detrainment in the mixed layer are determined by wind stirring and cooling at the oceanic surface, as in the Kraus and Turner (1967) model. The dynamic layer is a 1½‐layer model which allows entrainment due to shear instability at the base of the layer, similar to the Pollard et al. (1973) model. Monthly climatological data, along with the model sea surface temperature (SST), are used to determine the wind stress and heat fluxes forcing the model. The model is very successful in simulating the observed SST patterns, generally differing by no more than 0.5°C. During the Southwest Monsoon (June‐September),Tmdecreases markedly near Somalia and the Arabian peninsula owing to the entrainment of cool subsurface water at the coast and its subsequent advection offshore; farther offshore in the central Arabian Sea it decreases owing to increased evaporative cooling. During the Northeast Monsoon (December‐March), the decrease inTmis caused in part by reduced solar radiation and by increased evaporative cooling, with additional cooling by entrainment in the northern Arabian Sea. An interesting observed feature is that there is a net annual surface heat flux into the Arabian Sea. In the western Arabian Sea this flux is a direct result of coastal upwelling during the Southwest Monsoon, the cold water reducing the latent heat flux out of the ocean. In the central and eastern Arabian Sea it is caused by the southward advection of this upwelled water toward the equator. The annual heat and mass budgets are closed by equatorial currents: a westward undercurrent is the source of cool subsurface water that is entrained in the Arabian Sea, and a warm eastward surface current removes the excess heat and entrained water from the up

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16097

年代:1989

数据来源: WILEY

摘要:

Time series of the zero wind stress curl latitude and of the zonally averaged wind stress curl magnitude are used to drive volume transport in a linear, one‐layer, quasi‐geostrophic numerical model with a Drake Passagelike gap. The wind stress curl time series, computed from observed winds and low‐pass filtered to retain only seasonal time scales, are used to test the hypothesis that changes in the latitude of zero wind stress curl influence volume transport fluctuations through Drake Passage. Model results show that variations in the latitude of zero wind stress curl are coherent and in phase with model volume transport at periods greater than 30 days. When the time series of the latitude of zero wind stress curl are analyzed with transport accelerations both from the model and from Drake Passage observations, coherence squared between acceleration and the integrated wind stress curl are good. Both model experiments and Drake Passage field measurements suggest that variations in the latitude of zero wind stress curl are an important mechanism in modifying volume transport fluctuations in the Antarctic Circumpolar Cu

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16115

年代:1989

数据来源: WILEY

摘要:

Historical hydrographic observations have been composited and objectively analyzed for the North Atlantic Ocean for two pentads, 1955–59 and 1970–74, for the purpose of studying the temporal variability of the thermohaline structure of the deep North Atlantic Ocean. Statistically significant differences between the two pentads are found in the deep ocean. At 1750 m depth most of the North Atlantic increased in temperature (approximately 0.1°C) and salinity (0.025‰) from the earlier to the later period. An exception to this was a region in the eastern Atlantic between 33°N and 50°N where a cooling (0.1°C) and freshening (0.025‰) occurred. Changes at other depths as evidenced by difference fields of temperature along 24.5°N and 36.5°N are in agreement with differences found by Roemmich and Wunsch (1984) who described changes at these latitudes between sections taken in the late 1950's and sections

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16125

年代:1989

数据来源: WILEY

摘要:

This study presents evidence that the Azores Current (AZC) is a permanent feature of the North Atlantic subtropical gyre and that it feeds the North Equatorial Current (NEC). The AZC path is located south of the Azores; its velocity is mostly geostrophic, and the energy level in the mesoscale range is higher than in the NEC. The NEC velocity appears to be mostly ageostrophic, and the wind driven surface velocity is at about 15° to the right of the mean wind field

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16133

年代:1989

数据来源: WILEY

摘要:

A method of water mass analysis is developed which optimizes the use of all information contained in a hydrographic data set by solving an overdetermined linear set of mixing equations. It requires representation of water masses by a finite number of water types and observations from at least as many oceanographic parameters as water types. The procedure to establish the water types, find the correct weights for the parameters, and solve the mixing equations through minimization of the residuals is described in detail. The method is applied to a data set from the eastern Indian Ocean, where Indian Central Water and Australasian Mediterranean Water meet to produce a strong front in the thermocline. It is shown that although most of the water from the Indonesian archipelago is carried westward north of 11°S, contributions from the Australasian Mediterranean Water are found as far south as 25°S, particularly along the Australian shelf as a result of advection with the Leeuwin Curren

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16141

年代:1989

数据来源: WILEY

摘要:

A numerical model of marginal ice zones is presented which includes ice‐atmosphere‐ocean interactions and couples biological processes to the physical dynamics of the ice edge. We have used initial conditions from the Fram Strait in spring when stratification is increasing, nutrient concentrations are high, and solar radiation is increasing, conditions which are found prior to an ice edge phytoplankton bloom. We present three sets of experiments: (1) a standard case (and variations resulting from different initial conditions) with oceanic and ice melt stratification, but no winds or eddies, (2) one with wind forcing and ice cover but no eddies, and (3) cases with cyclonic and anticyclonic eddies under ice cover. In general, stratification within the upper layers accelerates the growth and accumulation of phytoplankton. When the stratification is due to ice melt only, the bloom is horizontally constrained between the ice and the ice edge frontal structure. Maximum primary productivity occurs 7 to 10 days after the introduction of stratification, and chlorophyll reaches a maximum approximately 3 days later. The bloom's biomass is eventually limited by nutrients. Wind‐driven ice edge upwelling alone was ineffective in stimulating phytoplankton growth. However, any wind‐induced horizontal movement of ice either uncovers nutrient‐rich water or advects nutrients into open water, which stimulates phytoplankton growth. When a cyclonic eddy rotates under the ice, a surface divergence results, causing the ice to open in the center, while upwelling at the eddy core injects nutrients into the euphotic zone. Anticyclonic eddies induce downwelling at the eddy's core and upwelling and surface divergence at the outer edges. With the increased irradiance and high nutrient concentrations, phytoplankton biomass within the eddy increase

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16151

年代:1989

数据来源: WILEY

摘要:

A new technique is used to calculate the modulation of the radar cross section of the ocean surface by a long gravity wave having a single narrow‐band spectral peak. Spectral analysis of the measured wave height time series is used to determine the position on the dominant wave illuminated during each radar sample. When we average the samples of the signal power received from the same phase position (but during different cycles) on the long wave, the phase‐interference (Rayleigh) fading is greatly reduced. The result is a measurement of the average radar cross section of the ocean surface as a function of the position on the long wave. The technique was applied to experimental runs where the radar beam was parallel to the crest of the dominant wave (cross‐wave look direction). Significant modulation was observed at both C and X bands, although there was no tilt modulation. A scenario where hydrodynamic and aerodynamic effects give rise to the modulation is discussed. “Sea spikes” occurred primarily near the front face of the long wave, with some also appearing immediately after the crest has passed, supporting the theory that they are often associated with the breaking of ripple waves riding near the top of the

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16177

年代:1989

数据来源: WILEY

摘要:

High resolution directional wave spectrum data were obtained from two NASA airborne radars during the Frontal Air‐Sea Interaction Experiment (FASINEX) in February 1986. The observations show a significant change in the wave number spectrum across the front. On the basis of surveys from a towed sensor and on satellite imagery, the front location and current field are estimated. A numerical model is developed for the wave‐current interaction and is used to model the wave refraction across the frontal current. A parametric study is performed to demonstrate the effects of current meandering. The main consequence of meandering is the formation of caustics and shadow zone regions in which the wave energy is significantly enhanced or reduced. Spectral simulation along the aircraft track reveals a reduction of more than 60% in wave energy in the shadow zone; this is consistent with the observati

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16189

年代:1989

数据来源: WILEY

摘要:

Controlled laboratory experiments have been conducted to study the kinematics of wave‐current interactions. The results confirm the conservation of waves under the steady state condition. The data also show that the kinematic effect of the current on waves can be treated as a simple Doppler shift. After the Doppler correction, the kinematics of the waves (either breaking or nonbreaking) follows the linear theory very well. The experiments also confirm the blockage of the waves by currents when the ratioū/C0approaches

ISSN:0148-0227    

DOI:10.1029/JC094iC11p16201

年代:1989

数据来源: WILEY