ISSN:0148-0227    

DOI:10.1029/JC091iC01p00801

年代:1986

数据来源: WILEY

摘要:

Profiles of the rate of viscous dissipation of kinetic energy in a Gulf Stream warm‐core ring show large rates in the thermocline and in the entrainment region near the edge of the ring. The thermostad has very low levels of dissipation except where that region is in contact with the Gulf Stream. Dissipation rates in the thermocline are independent of the large scale vertical shear and are consistent with the concept of near‐inertial wave trapping by the ring's geostrophic shear. Near the edge, to depths of 1000 m, turbulence is associated with entrainment and interleaving. Thee‐fold decay scale for the dissipation of the ring's total energy is 2 to 3 years, but is only 140 days for the kinetic energy, so energy conversion from potential to kinetic must be occurring on time scales of 10 to 30 days. The vertical eddy diffusivity of the ring is 0.1 × 10−4m2/s except in the thermostad where it is smaller by approximately a factor of 10. The eddy viscosity is more than 10 × 10−4m2/s; hence tubulent diffusion is relaxing the velocity field faster than the th

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00803

年代:1986

数据来源: WILEY

摘要:

This study is aimed at modeling mesoscale processes such as upwelling/downwelling and ice edge eddies in the marginal ice zones. A two‐dimensional coupled ice‐ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model through interfacial stresses. The parameters of the ocean model were chosen so that the dynamics would be nonlinear. The model was tested by studying the dynamics of upwelling. Winds parallel to the ice edge with the ice on the right produce upwelling because the air‐ice momentum flux is much greater than air‐ocean momentum flux; thus the Ekman transport is greater under the ice than in the open water. The stability of the upwelling and downwelling jets is discussed. The downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence. A constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling/downwelling regions, i.e., wind‐forced vortices. Steepening and strengthening of vortices are provided by the nonlinear terms. When forcing is time‐varying, the advection terms will also redistribute the vorticity. The wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underne

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00819

年代:1986

数据来源: WILEY

摘要:

A detailed survey of radon 222 and temperature profiles of the benthic boundary layer in the Hatteras Abyssal Plain shows a strong correlation between the structure of both. The apparent vertical diffusivities estimated from radon 222 are of the order of 50 cm2s−1in the mixed layer, and of the order of 1 cm−2s−1above it. One profile appears to have been taken in a frontal zone where isotherms dip sharply into the sediments. This is the only profile where there is significant penetration of radon above the mixed layer. Several other profiles suggest that the temperature may take longer than several radon half‐lives to adjust to new mixing and advection regimes. In such cases, one often sees considerable structure in the radon profile within the region where the potential temperature is wel

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00833

年代:1986

数据来源: WILEY

摘要:

We present evidence for a narrow, poleward flowing surface current over the continental slope of northwestern British Columbia and southwestern Alaska. Named for a prominent native Indian tribe of the region, the Haida Current occurs predominantly between October and April. Maximal flow takes place in midwinter from November through February. Characteristic features of the current include a minimal extent of 200–300 km, a width of 20–30 km, a depth scale of 500 m, and near‐surface temperature signatures of up to +1°C within the core of the current, as well as large‐amplitudeO(10 km) mesoscale waves and eddies along its flank. The wind stress and alongshore sea surface slope are shown to be the primary driving mechanisms for the

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00845

年代:1986

数据来源: WILEY

摘要:

The seasonal variability of the wind stress curl over the North Atlantic is investigated by means of empirical orthogonal function (EOF) analysis. The curl field is calculated from 1 year of First Global GARP Experiment wind data. It was found that 44% of the variability is contained in four significant eigenvectors. Their spatial patterns are characterized by basin‐sized oscillations with larger amplitude to the north of 40°N. Their associated time series coefficients have the highest amplitude during the winter and show a tendency toward a white frequency spectrum which nevertheless exhibits noticeable peaks or gaps at certain frequencies. Physically, the first EOF is seen as the seasonal fluctuations of the mean wind stress curl pattern. Five other eigenvectors are also found to be above the noise level, but they account for only a smaller percentage of variability (19%). They are characterized by smaller spatial scales than the basin size. Their time series coefficients show a whiter frequency spectr

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00863

年代:1986

数据来源: WILEY

摘要:

Lake Biwa in Japan has a stable cyclonic gyre during seasons of thermal stratification. A vertical circulation consisting of downwelling in the central area and upwelling near the rim of the gyre is calculated by the diagnostic model. The energetics in the model indicate that this vertical circulation corresponds to the decay process of the gyre. Tracking of drifters in summer supports the presence of a vertical circulation, though its magnitude is about 50% less than that estimated by the diagnostic model. This is explained from the ratio of kinetic energy and available potential energy of the gyre. The realistic value of the vertical eddy viscosity is estimated to be 0.8–2.1 cm2s−1in summer. Monthly variations of the horizontal and vertical circulations are calculated by the diagnostic model using the monthly mean density fields. The gyre and the vertical circulation are maximal in September. The characteristic decay time scale of the gyre is estimated to be about 10 days. The effect of topographic differential heating is considered to be one of the maintenance mechanisms of the gyre in early summer, and the wind stress curl to be the important maintenance force for the gyre from late summer to late f

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00869

年代:1986

数据来源: WILEY

摘要:

During spring and early summer 1983, fifteen current moorings were deployed around the periphery of Santa Barbara Channel and over the continental shelf to the west, off Point Conception. Data from these moorings have been used to describe the regional circulation and to address problems of wind forcing and the spatial coherency scales for current fluctuations. The mean circulation in Santa Barbara Channel was dominated by a westward jet which occupied the northwestern portion of the Channel. Current and temperature fluctuations were generally well‐correlated among all locations around the Channel, and time lags suggested cyclonic propagation of events around the Channel. The time fluctuations were dominated by a relatively few low‐frequency events. It was impossible to determine exactly either the driving mechanisms for these events or their relationships to regional flow. The flow regime was considerably different off Point Conception than in the Channel. Locally wind‐driven upwelling was observed in both the mean and fluctuating flows, and the time scales of current variability (i.e., spectral shapes) mimicked those of the local winds. A dramatic change in the regime off Point Conception occurred in late May. Before the transition, currents and sea levels had been well correlated in time with both local and remote winds. After late May the relation to fluctuating winds was less clear and the alongshore structure of sea level variability had changed radi

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00877

年代:1986

数据来源: WILEY

摘要:

The atmospheric flux of cosmogenic7Be (53.3‐day half‐life) and the mode of7Be deposition in river‐estuarine and coastal environments have been examined. The atmospheric flux of7Be commonly supports inventories ranging from 1.0 to 2.0 pCi/cm2(1 pCi = 0.037 Bq). Beryllium 7 concentrations in water phase samples, collected across salinity gradients in several estuaries along the eastern coastline of the United States, range from 0.03 to 0.53 pCi/L and primarily reflect variations in7Be supply and sorption kinetics. The major process controlling the concentration of7Be on estuarine suspended particles appears to be the length of time that these particles remain in the water column. Field particle‐to‐water distribution coefficients for7Be have a median value of about 4 × 104but range over an order of magnitude reflecting short‐term variations in7Be input, particle dynamics, and particulate iron content rather than equilibrium sorption‐desorption responses to changes in water salinity or particle type. Residence times of7Be in the water column range from a few days in estuarine areas of rapid fine‐particle deposition, to several weeks in high‐energy environments where pronounced sediment resuspension reintroduces deposited7Be back into the water column. Inventories of7Be in sediments range from nondetectable to 3.3 pCi/cm2, with the highest inventories in areas where fine particles are accumulating rapidly. Such sites are also major repositories for other particle‐reactive substances. A7Be budget for the James estuary indicates that less than 5% of the expected7Be input is in the water column and that the short‐term estuarine trapping efficiency for atmospherically derived7Be is somewhe

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00896

年代:1986

数据来源: WILEY

摘要:

On July 19, 1980, 80% of the runoff of Eastmain River, a subarctic shallow estuary, was diverted into the La Grande River for hydroelectric development. Consequent to the diversion, the estuary, which had been mostly salt‐free, was subjected to a gradual saltwater intrusion along a 10‐km section in its lower reaches. The adjustment of the salinity regime to a new quasi‐steady state took place over a period of about 40 days. The circulation field reached a new quasi‐equilibrium within 8 days. The 2‐month interval following the river diversion, termed the transition period, was analyzed in terms of both time and space modifications of the circulation and salinity fields. A one‐dimensional finite difference explicit scheme numerical model was applied to the estuary as a complement to observational data. Good agreement was obtained between the model results and the low‐frequency current meter observations of salinity and longitudinal velocity. These results showed that the salinity intrusion was primarily governed by tid

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00909

年代:1986

数据来源: WILEY