ISSN:0148-0227    

DOI:10.1029/JC089iC01p00569

年代:1984

数据来源: WILEY

摘要:

The influence of oceanic heat transport on the sensitivity of climate to an increase of the atmospheric CO2concentration is studied by comparing the CO2‐induced changes of two mathematical models. The first model is a general circulation model of the coupled ocean‐atmosphere system which includes ocean currents. In the second model the oceanic component of the first model is replaced by a simple mixed layer without ocean currents. Both models have limited computational domain with idealized geography and annual mean insolation. For each model, the sensitivity of climate is evaluated from the difference between the equilibrium climates of the normal CO2and 4 times the normal CO2concentrations. The results indicate that the presence of ocean currents reduces the sensitivity of surface air temperature because of the difference in magnitude of the surface albedo feedback effect. The poleward transport of heat by ocean currents raises the surface temperature at high latitudes, shifts poleward the margins of snow and sea ice, decreases the contribution of the albedo feedback effect, and reduces the sensitivity of climate. The equilibrium response of climate is compared with the transient response of climate to a sudden increase of atmospheric CO2content. According to this comparison, the latitudinal dependence of the equilibrium response of zonally averaged surface temperature is qualitatively similar to the transient response approximately 25 years after the time of the sudden CO2increase. This result suggests that the distribution of the zonally averaged temperature change in response to a gradual increase of atmospheric carbon dioxide also resembles the distribution of the equilibrium response provided that the characteristic time scale of the CO2increase is longer than 25 ye

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00571

年代:1984

数据来源: WILEY

摘要:

Satellite and hydrographic observations obtained during May 1981 are used to examine the sea surface and subsurface temperature structures within a portion of the Tohoku Area (38°–43°N) extending east of Japan to 149°E longitude. These data delineate the Oyashio Front and the evolution of mesoscale features dominating the surface layer circulation east of northern Honshu and Hokkaido. A perturbation on the first Oyashio Intrusion generated eddies adjacent to the Oyashio Front and contributed to a jetlike feature with associated, paired vortices that intruded into what has been defined as the “perturbed area” (39°–42°N) southeastward from the vicinity of the Tsugara Strait. NOAA6 satellite Advanced Very High Resolution Radiometer infrared images and sea surface temperature distributions identified specific eddies and fronts, that also appeared as banded warm and cold regions within XBT (expendable bathythermograph) sections. The satellite data helped define the lateral extent of the features, while the sections provided estimates of their vertical extent. A new procedure for the determination of satellite sea surface temperatures was used to produce a composite temperature distribution over a portion of the Tohoku Area. The satellite‐derived temperature estimates exhibited a 0.8°C rms scatter about a 0.6°C warm bias relative to the XBT data. This map displays the intense mesoscale sea surface temperature variability in the region along the Oyashio Front and within the

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00587

年代:1984

数据来源: WILEY

摘要:

The warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well‐mixed conditions predominate in the southeastern part of the sub‐ice‐shelf cavity where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m/yr and will drive a thermohaline circulation having the following characteristics: high salinity shelf water (at −1.8°C), formed by winter sea‐ice production in the open Ross Sea, flows along the seabed toward the tidal mixing fronts below the ice shelf; and meltwater (at −2.2°C), produced in the well‐mixed region, flows out of the sub‐ice‐shelf cavity along the ice shelf bottom. Sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea‐surface

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00597

年代:1984

数据来源: WILEY

摘要:

Tidal currents below the floating Ross Ice shelf are reconstructed by using a numerical tidal model. They are predominantly diurnal, achieve maximum strength in regions near where the ice shelf runs aground, and are significantly enhanced by topographic Rossby wave propagation along the ice front. A comparison with observations of the vertical motion of the ice shelf surface indicates that the model reproduces the diurnal tidal characteristics within 20%. Similar agreement for the relatively weak semi‐diurnal tides was not obtained, and this calls attention to possible errors of the open boundary forcing obtained from global‐ocean tidal simulations and to possible errors in mapping zones of ice shelf grounding. Air‐sea contact below the ice shelf is eliminated by the thick ice cover. The dominant sub‐ice‐shelf circulation may thus be tidally induced. A preliminary assessment of sub‐ice‐shelf conditions based on the numerical tidal simulations suggests that (1) strong barotropic circulation is driven along the ice front and (2) tidal fronts may form in the sub‐ice‐shelf cavity where the water column is thin and where the buoya

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00607

年代:1984

数据来源: WILEY

摘要:

The motion of suspended sand particles is studied by means of a new perturbation solution to the equation of motion. In the first approximation, fluid accelerations are neglected so that the relative velocity between sand and water is everywhere equal to the still water settling velocity . It turns out that some of the most important mechanisms of sediment suspension, such as trapping in vortices, can be derived from this “zero order solution” when the flow structure is given proper consideration. The next level of solutions takes into account the effect of fluid accelerations by including terms of order of magnitude. As a main result it is shown that pure wave motion does not cause a net reduction of settling velocity of this order of magnitude. Finally the effect of drag nonlinearity is studied for the case of an oscillatory flow. It is shown that this effect is of the order of magnitude ε2and without practical importance for sediment suspension by w

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00616

年代:1984

数据来源: WILEY

摘要:

Laboratory experiments were conducted in a wind‐wave tank to study the turbulence characteristics in the air and wave boundary layers generated by wind and waves. The turbulent air boundary layer over the water surface was surveyed using two hot‐wire probes. It was found to be a good simulation of an atmospheric boundary layer over a body of water. Capacitance probes were used to record the wave height. Spectra, wave phase velocity, dominant wavelength and frequency, and other statistics of the wind waves were computed. The water boundary layer below the water surface was surveyed using an array of 10 cross‐element hot‐film probes to measure the stream wise and vertical components of velocity. Various turbulence statistics including mean velocity, root‐mean‐square velocity fluctuations, Reynolds stress, dissipation rate, spectra, and higher‐order statistics were computed. Similarity profiles were found for the mean subsurface current and the rms turbulent fluctuations in the streamwise and vertical directions. The velocity spectra indicated the relative importance of the wave‐induced motion, which attenuated ex‐ponten

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00627

年代:1984

数据来源: WILEY

摘要:

Observations from theSomovduring the US‐USSR Weddell Polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60°S Greenwich meridian region has an oxygen content of 7.4 ml/1. This is 86% of full oxygen saturation, representing an oxygen deficit, relative to full saturation, of 1.1 ml/1. The source of this deficit is believed to be a consequence of oxygen‐poor (4.5 ml/1) Weddell Deep Water (WDW) entrainment by the winter mixed layer. Assuming effective cutoff of ocean‐atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors, a mixing ratio of 1:3 for WDW to “beginning of winter” surface water is required to explain the end‐of‐winter mixed‐layer oxygen content. Accompanying the WDW transfer into the mixed layer is heat transfer of approximately 7×103cal/cm2(2.9×108J/m2) during the five winter months of sea ice coverage as well as salt transfer, which requires 34 cm of fresh water to produce typical mixed‐layer salinity. During the seven ice‐free months when entrainment is expected to be minor, diffusive heat and salt flux continues. A mean annual heat flux of 12 W/m2is suggested, with an annual demand for freshwater of 46 cm/yr. Consideration of the winter period salinity budget indicates net sea ice melting of 20 cm, which can be attributed to regional convergence of sea ice. The remaining freshwater is derived from excess precipitation and possibly iceberg melt. Oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a ful

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00637

年代:1984

数据来源: WILEY

摘要:

The end of winter stratification within the cold cyclonic trough of the Weddell gyre near 60°S between 5°E and the Greenwich meridian is resolved with theMikhail Somovdata set. The temperature maximum of the Weddell Deep Water (WDW) is, for the most part, less than 0.5°C, but warmer cells of WDW are found. These warm WDW cells have temperature, salinity, and oxygen properties similar to the WDW characteristic of the Weddell gyre inflow, which is situated to the southeast of theMikhail Somovstudy region. The warm WDW cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline, while deeper isopycnals are depressed. Anticyclonic shear below the 27.83 σ‐θ isopycnal within the warm WDW cells is compensated by the cyclonic shear associated with the pycnocline dome. The pycnocline domes are exposed to about 50% greater entrainment by the turbulently active winter mixed layer, relative to the regional entrainment rate. This entrainment can significantly erode the warm cells in a single winter season, introducing excess heat and salt into the mixed layer. While the heat is lost to the atmosphere, the excess salt is not necessarily compensated by increased fresh water introduction. It is hypothesized that the warm WDW cells within the Weddell gyre trough are derived from instability within the frontal zone which extends from Maud Rise to the northeast, separating the Weddell warm regime from the cold regime. Greater than normal injection of warm WDW cells into the Weddell gyre trough would increase the surface salinity, which would tend to destabilize the pycnocline, increasing the probability of deep convection and polynya

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00641

年代:1984

数据来源: WILEY

摘要:

During a traverse of the Antarctic marginal ice zone (MIZ) near the Greenwich Meridian in October 1981, we launched a series of radiosondes along a 150‐km track starting at the ice edge. Since the wind was from the north, off the ocean, these radiosonde profiles showed profound modification of the atmospheric boundary layer (ABL) as the increasing surface roughness decelerated the flow. The primary manifestation of this modification was a lifting of the inversion layer with increasing distance from the ice edge by the induced vertical velocity. But there was also a cooling of the stably stratified mixed layer below the inversion and a consequent flux of sensible heat to the surface that averaged over 200 W/m2. The magnitude of this flux suggests that atmospheric heat transport plays a significant role in the destruction of ice in the Antarctic MIZ. Using the rising of the inversion and ABL similarity theory, we estimated the change in the neutral stability drag coefficient,CD, across the MIZ.CDincreased from its open ocean value, 1.2×10−3, at the ice edge to 4.0×10−3at 80–90% ice concentration. We present an equation for this dependence of drag on ice concentration that should be useful for modeling the surface stress in marginal

ISSN:0148-0227    

DOI:10.1029/JC089iC01p00649

年代:1984

数据来源: WILEY