摘要:

Two polynyas over the deep ocean were observed in the Antarctic region during the winter of 1980: one near 43°E, 66°S (Cosmonaut polynya) and another near 2°E, 64°S (Maud Rise polynya). The time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the Nimbus 7 scanning multichannel microwave radiometer (SMMR). A quantitative analysis of a study area around it shows that the totally enclosed Cosmonaut polynya attained a maximum size on July 25, 1980, with an open water area of as much as 137,700 km2. This polynya lasted for a few weeks, disappeared on August 16, 1980, and was not observed for the rest of the winter. Similar polynyas in the same region have occurred for several years, including 1973, 1975, 1979, 1982, and 1986. The Maud Rise polynya, on the other hand, was observed as a reduction in ice concentration to about 37% within the SMMR resolution of about 900 km2. However, the open water area in the region amounted to 92,800 km2on July 20, and the polynya recurred several times during the same winter period. It is proposed that both polynyas are products of deep‐reaching convection which introduces warmer deep water into the surface layer. In this way, they are viewed as sensible heat polynyas in that they are maintained by oceanic heat. The oceanographic settings of these two polynyas are similar. The hydrographic data at both sites indicate the existence of localized doming of the pycnocline. This brings warmer, saltier deep water closer to the sea surface, which has been demonstrated to be an effective preconditioner for deep‐reaching convection. It is probable that the polynyas are terminated by “invasion” of sea ice from the sides, which attenuates convection. The capability of a polynya to survive an entire winter period may be related to its size; the larger polynyas are better protected from convergence of the surrounding sea ice. For example, a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02819

年代:1987

数据来源: WILEY

摘要:

Long waves appeared at a zonally oriented sea surface temperature (SST) front in the eastern equatorial Atlantic during June and July of 1983. The low frequency, westward moving long waves (1000 km, 24 days) are monitored in the NOAA 7 satellite infrared images as meridional displacements of the front. The long waves observed in the Atlantic are similar to the waves previously seen in the eastern equatorial Pacific with several exceptions. The Atlantic long waves have a shorter duration (nearly three wave cycles at 15°W), and the wave amplitude is limited eastward of longitude 10°W. The Atlantic equatorial front appears to have a minimum north‐south displacement between longitudes 5°W and 10°W, while westward of 10°W the displacements exceed 400 km. Several buoys were launched south of the equator at longitude 4°W by the Programme Français Océan‐Climat en Atlantique Equatorial group on June 21, 1983. For the first 3 weeks, three of the buoys moved westward parallel to the equatorial SST front and measured relatively constant temperatures at 2 m. During mid‐July, changes were observed in the buoy temperatures, the buoy trajectories, and the long‐wave pattern. A comparison of the buoy temperatures at a depth of 2 m and atmospherically corrected satellite estimates of SST show a residual dependence of the satellite data on the zenith angle, even when the angle is limited to 45°. In general, the satellite SST measurements reproduce the trends observed in the buoy measurements, but small bias differences occur between buoys and between day and nighttime SST comparisons. Equatorial cross sections by ship and satellite over a 7‐day interval in June 1983 also show that SST trends are comparable in

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02835

年代:1987

数据来源: WILEY

摘要:

An approximate temperature perturbation equation for a continuously stratified deep ocean layer on an equatorial β plane is presented. A vertically integrated flow is allowed, which in the present study is forced by uniform upwelling. Solutions with truncated vertical structure are presented which are forced by a representation of localized geothermal heat sources. Solutions exhibit a range of behavior from passive advection to β plume, depending on the ratio of barotropic flow speed to long Rossby wave phase speed. Owing to the different phase speeds of the vertical modes, the forced vertical structure is dispersed, which can result in positive and negative temperature anomalies both upstream and downstream of the source. Furthermore, it is clear that the ability of localized sources to influence “upstream” conditions is enhanced in equatorial regions compared with higher latitudes, where the background flow is better able to advect the temperature perturbations downstream. Depending on the strength of the imposed temperature anomaly at the source, there may or may not be a large‐scale reversal of the total flow field. Thus the correlations between temperature, geostrophic shear, and a passive tracer such as3He can be positive, negative, or zero away from the geothermal

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02843

年代:1987

数据来源: WILEY

摘要:

In an effort to measure current shear very near the sea surface a string of vector‐measuring current meters suspended beneath a surface float was deployed 180 km off southern California at 34°N 121°30′W on November 26, 1981 and allowed to drift freely for over 6 days. This arrangement, which we call the current meter drifter (CMD), gave measurements at depths of 2.5, 5.5, 8.5, 11.5, 14.5, 25, and 63 m. During the first two days, when the winds were light (≃8 m/s) and variable in direction, a nearly uniform current shear was observed in the upper 15 m with a low‐frequency velocity difference of 5 cm/s between the instruments at 2.5 and 14.5 m. During the last four days, when the winds were brisk (>12 m/s) and steady in direction from the NNW, a strong downwind shear of order 10−2s−1was observed in the upper 10 m with a velocity difference of ∼7 cm/s between the instruments at 2.5 and 8.5 m. During this same period the shear below 10 m was much smaller. The average currents during the CMD drift veer to the right of the wind stress with angular displacement increasing with depth. Time series of the velocity difference between 2.5 and 5.5 m compare very well with θ(t)u*κ−1ln (5.5/2.5), where θ(t) is the wind direction vector (of unit magnitude),u*= (wind stress/ρ)½is the friction velocity in water, and κ = 0.4 is von Karman's constant. On the other hand, a similar comparison of the velocity difference between 5.5 and 8.5 m to θ(t)u*κ−1In (8.5/5.5) is much poorer with observed velocity difference being much larger, possibly due to stable stratification effects. Possible errors in the measurements have been considered and estimated as less than the observed velocity differences. Near‐surface shears as large as the observed are very important in closing the momentum budget f

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02851

年代:1987

数据来源: WILEY

摘要:

Sea surface temperatures (SSTs), computed from sensor systems on the National Oceanographic and Atmospheric Administration (NOAA) polar‐orbiting satellites, are compared with surface skin temperatures (from an infrared radiometer mounted on a ship) and subsurface temperature measurements. Three split window retrieval methods using channels 4 and 5 of the NOAA 7 advanced very high resolution radiometer (AVHRR) sensor were investigated. These methods were (1) using AVHRR alone, (2) using AVHRR with atmospheric temperature and water vapor profiles from the TIROS operational vertical sounder (TOVS), and (3) using AVHRR and data from the high‐resolution infrared sounder (HIRS). TOVS sensors (including HIRS) are carried by the same satellite as the AVHRR and provide simultaneous corrections for the AVHRR‐based SST estimates. The importance of scan angle correction to define the correct atmospheric path is discussed, and the improvement of SST retrievals using sensor combinations is demonstrated with satellite versus ship skin temperature mean differences ranging from 0.55° to 0.73°C for AVHRR alone, from −0.39° to 0.71°C for AVHRR plus TOVS, and from 0.22° to 0.33°C for AVHRR plus HIRS. The improved SST accuracy by AVHRR plus HIRS is due to additional correction for the atmospheric water vapor and temperature structures, made possible with some of the HIRS channels. Significant differences between ship skin and subsurface temperatures were observed, with the mean deviation being 0.2°C for a range of temperature differences between

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02859

年代:1987

数据来源: WILEY

摘要:

Acoustic backscatter images obtained at 107 and 200 kHz of surge‐type turbidity currents resulting from mine tailing discharge are presented. Excess densities in the head of the order of 100 kg m−3are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom‐reflected signal. These excess densities are comparable to estimates based on surge height and speed, the speed being determined by assuming a universal head shape. Unlike gravity current surges from an impulsively started steady source, the surge‐type turbidity flows consist of a high concentration slug of short duration followed by a longer‐lived wake in which sediment concentrations are lower by 2–3 orders of magnitude. The profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments. Discrete scatterers, probably fish, are observed to avoid

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02875

年代:1987

数据来源: WILEY

摘要:

Acoustic backscatter images are presented of the continuous flow turbidity current resulting from mine tailing discharge into Rupert Inlet. The current flows partially within a submarine channel, which both hooks to the left and meanders. The images show the turbidity current spilling over the outer levees at channel bends. A model for continuous turbidity flow incorporating overspill is developed and applied to the left‐hooking section of the submarine channel. It is very likely that the observed overspill is primarily an inertial effect resulting from the outer bank being more sharply curved than the channel axis. The model results are combined with a sediment accumulation budget based on successive seismic profiling surveys and with results for surge‐type flows (taken from the companion paper (Hay, this issue)). It shows that surges are primarily responsible for the transport of tailing to large distances from the point of discharge and should recur at 1‐ to 2‐day intervals on average. This is consistent with the characteristics of coarse‐grained turbidites observed in cores from the levees. Relative to the intervening fine‐grained mud deposits the turbidites increase both in thickness and frequency in the downchannel direction. Furthermore, the surge recurrence interval obtained from the number of turbidites per core and the local accumulation rate is 2–5 days, essentially the same as that obtained from the model. Suspended tailing transport within the channel appears to be dominated by surge‐type turbidity currents except close to the outfall. It is concluded that the surge‐type flows are most responsible for the formation and morphology of much of the channel. It is not clear, however, that the meanders are formed principally by surges. Although the surges occur frequently and transport most of the sediment in the meander reach, the volume transport is dominated b

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02883

年代:1987

数据来源: WILEY

摘要:

In 1973 Stommel et al. predicted that the Western Mediterranean Deep Water (WMDW) contributes directly to the Mediterranean outflow through the Strait of Gibraltar (Strommel et al., 1973). Hydrographic data obtained in November 1985 showed unambiguous evidence of WMDW west of the major Gibraltar sill, thus confirming the prediction.

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02901

年代:1987

数据来源: WILEY

摘要:

We present an inverse method that uses measurements of the concentration of several tracer variables to find the mixture of source water types that best describes (in a weighted least squares sense) the composition of the water sample. The solution includes two physically realistic constraints: first, that all sources together must sum to 100% and, second, that no source is present in negative amounts. These constraints improve the statistical stability of the solution. The method is particularly valuable in regions involving strong mixing among a relatively large number of source water types. In contrast to conventional TS analysis, more water types can be considered, the assumption of mixing along isopycnals is unnecessary, and sensitivity to errors in individual tracer measurements is reduced by averaging the influence of a larger number of tracers. We demonstrate the method using data from two oceanographic regions. Analysis of summer data from the continental margin off Vancouver Island (British Columbia, Canada) confirms and quantifies the importance of deep upwelling of California Undercurrent water onto the continental shelf. It also identifies localized outer shelf filaments of low‐salinity water originating from the Vancouver Island Coastal Current. Finally, we reanalyze the North African data of Tomczak and confirm his interpretation of diapycnal mixing at the frontal boundary between North Atlantic Central Water and South Atlantic Central Water masse

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02907

年代:1987

数据来源: WILEY

摘要:

In order to estimate ocean‐atmosphere mass transfer fluxes controlled by aerosol generation the bubble population at the interface has to be known. This information is usually inferred from measurements at a given depth below the water surface and from broad assumptions about the variation of bubble population with depth. However, recent measurements are not consistent with the usually assumed bubble population variation, and a direct investigation in the immediate vicinity of the interface appears to be necessary. Measurements above the minimum wave trough are difficult because a sensor level is alternately in the air and in the water. We have used a laser‐based single‐particle technique to investigate this zone for different breaking wave fields generated in a wind‐water simulation facility. The main bubble population characteristics, common to the different breaking wave fields investigated, are as follows: a roughly invariant size distribution characterized by a spectrum slope of approximately −2, concentrations rapidly increasing upward, following approximately an exponential law, and clustered distributions at the different measurement levels. These results, consistent with equivalent measurements below the wave trough level, correspond to bubble generation zone characteristics suggested in a previous investigation and provide further evidence of the existence of a universal bubble distribution at the interface of breaking wave fields. Very high bubble concentrations, up to 1010bubbles of diameter larger than 60 μ per cubic meter (nearly 10,000‐fold the value just below the trough level), are observed at the

ISSN:0148-0227    

DOI:10.1029/JC092iC03p02919

年代:1987

数据来源: WILEY