摘要:

The following three papers [Broecker et al., this issue;Smith and Jones, this issue;Wesely, this issue] are a detailed discussion between the oceanographic geochemical community and the physical oceanographic air‐sea interaction community. It is my opinion that these papers provide for the general scientific community an in‐depth review of the methods to estimate CO2fluxes across the sea surface.The differences between the two scientific groups were brought to my attention when we received the original manuscript submitted by and finally published bySmith and Jones[1985]. During the review process, all geochemists criticized the manuscript and all physicists applauded it. W. Broecker was invited to provide a response toSmith and Jones[1985] and they andWesely et al.[1982] were invited to provide replies toBroecker et al.[this iss

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10515

年代:1986

数据来源: WILEY

摘要:

Eddy correlation measurements over the ocean give CO2fluxes an order of magnitude or more larger than expected from mass balance measurements using radiocarbon and radon 222. In particular, Smith and Jones (1985) reported large upward and downward fluxes in a surf zone at supersaturations of 15% and attributed them to the equilibration of bubbles at elevated pressures. They argue that even on the open ocean such bubble injection may create steady state CO2supersaturations and that inferences of fluxes based on air‐sea pCO2differences and radon exchange velocities must be made with caution. We defend the global average CO2exchange rate determined by three independent radioisotopic means: prebomb radiocarbon inventories; global surveys of mixed layer radon deficits; and oceanic uptake of bomb‐produced radiocarbon. We argue that laboratory and lake data do not lead one to expect fluxes as large as reported from the eddy correlation technique; that the radon method of determining exchange velocities is indeed useful for estimating CO2fluxes; that supersaturations of CO2due to bubble injection on the open ocean are negligible; that the hypothesis that Smith and Jones advance cannot account for the fluxes that they report; and that the pCO2values reported by Smith and Jones are likely to be systematically much too high. The CO2fluxes for the ocean measured to date by the micrometeorological method can be reconciled with neither the observed concentrations of radioisotopes of radon and carbon in the oceans nor the tracer experiments carried out in lakes and in wind/wave tunn

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10517

年代:1986

数据来源: WILEY

摘要:

Clarifications of the interpretation of the CO2eddy flux measurements of Smith and Jones (1985) are offered in the context of criticisms by Broecker et al. (this issue). Downward pumping of CO2and other atmospheric constituents by the pressurization of air entrained by breaking waves is considered to be a plausible mechanism. Apparent discrepancies between short‐term “eddy flux” surface exchange rates and longer‐term isotopic determinations can be resolved if short‐term storage of dissolved gas in upper water layers is considered to influence only t

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10529

年代:1986

数据来源: WILEY

摘要:

Measurements of short‐term, local air‐sea exchange of CO2by eddy correlation in the atmosphere from surface towers have shown that the transfer (piston) velocities in coastal areas are very large in comparison to long‐term oceanic estimates from radioisotope studies. The latter agree with radon evasion and laboratory investigations involving nonreactive gases. Horizontal atmospheric advection seems to be the most likely source of significant error in the eddy correlation estimates but is probably not the cause of the large transfer velocities because they were measured in a wide range of conditions by independent investigators. Furthermore, extrapolation of the large transfer velocities measured by the eddy correlation measurements to world average air‐sea exchange rates does not provide a realistic basis on which to evaluate the validity of the local eddy flux measurements in coastal areas. Important chemical and physical phenomena affecting CO2exchange rates may be quite different in coastal as opposed to open‐ocean conditions, and further research is needed in b

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10533

年代:1986

数据来源: WILEY

摘要:

The seasonal variability of current velocities in the tropical Atlantic was studied by grouping ship drift velocity observations into 2° × 5° boxes and calculating monthly mean velocity values. These values were used to calculate and map the annual mean velocity, the seasonal variation about the mean, the annual and semiannual harmonics, and the first two empirical orthogonal functions (EOFs). The seasonal variation is primarily zonal in the equatorial band and in the North Equatorial Countercurrent (NECC) and primarily alongshore near the coast of South America. Maxima of seasonal variation of 23 cm/s are centered in the NECC near 6°N, 42.5°W and in the Gulf of Guinea near 2°N, 7.5°W. Most (∼80%) of the variance in the NECC and along the western boundary of the area studied has an annual period; most of the variance along the equator in the mid‐Atlantic has a semiannual period. Over the whole region, 49% of the seasonal variance is explained by the annual harmonic, and 69% is explained by a combination of the annual and semiannual harmonics. The second EOF contains 29% of the variance of the data set and shows a simultaneous speeding (slowing) of the major equatorial currents (the South Equatorial Current (SEC), the North Brazil Current, the NECC, and the Guinea Current) along their principal axes of variation with a concurrent slowing (speeding) of the Guyana Current and the Brazil Current. The pattern of variation resembles a large equatorial gyre centered along 4°N that flows clockwise from May to September and counterclockwise most of the rest of the year. The first EOF accounts for 35% of the variance and shows a simultaneous speeding (slowing) of eastward velocity from 5°S to 10°N except in the western SEC, the western end of the North Brazil Current, and the Guinea Current. The out‐of‐phase fluctuations apparent in the western SEC near the equator are explained by the slowing and reversal of the South Equatorial Current near 2°N, 40°W between April and June. This slowing of the SEC is associated with the start up of the NECC, which accelerates eastward in May, June, and July and flows eastward across the Atlantic from July through December. The SEC divides seasonally near the eastern tip of Brazil, where residual alongshore velocities are northward for half the year (peaking during May and June) and southward for the other half of the year. A second division can be seen north of the Amazon, where the North Brazil Current continues up the coast into the Guyana Current during the first half of the year but partially retroflects into the NECC during the last half of the year. A fast eastward flow in the NECC coincides with below average velocities in the Guyana Current and above average velocities in the western sections of the North Brazil Current and the SEC (no

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10537

年代:1986

数据来源: WILEY

摘要:

Two time series of wind speed have been inferred from ambient noise measurements obtained with bottom‐deployed inverted echo sounders in the southwestern Atlantic. Comparison between inferred winds and winds from the National Meteorological Center Tropical Strip Surface Analysis product establishes that there is a good agreement between the two observations. The wind records from the two instruments, deployed 181 km apart, show significant differences at low frequencies. The mean speed for the recorded period is 10 m/s. The energy density spectra of the inferred wind records show a decrease in energy with frequency with a slope of −1.7 for frequencies between 0.22 and 20 cpd. The analysis of the spectra from the time series at the two moored locations shows differences in the band 2–10 days. An increase in the variance is detected in the offshore location at discrete periods corresponding to atmospheric oscillations. These oscillations are considerably less energetic in the continental shelf‐slope regime but are coherent in both lo

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10551

年代:1986

数据来源: WILEY

摘要:

During 1978 and 1979, four experiments with clusters of 6 to 10 drifting buoys were carried out in the Atlantic Equatorial Undercurrent. The measurements were intended to estimate horizontal mixing and its possible contribution to the salt loss of the high‐salinity core related to the Equatorial Undercurrent. The buoys were drogued at the estimated depth of the salinity core of 70 m to 90 m. The diameters of the spreading clusters ranged from 3 to 10 km. Each experiment was maintained for about 2 days. During this period the buoys were tracked by radar from a nearby operating research vessel. From the observed tracks, horizontal turbulent mixing coefficients were deduced. The results show a dependence on the horizontal scale ofl1.43. This is not significantly different from an expectedl4/3law. Using the obtained scale dependence, the observations are extrapolated to the scale of the salinity core of 150 km obtained from hydrographic observations, resulting in a turbulent mixing coefficient of 6.5 × 106cm2s−1. Combining these numbers with the horizontal gradients of the salinity core, one obtains a salt loss of 1.42 g s−1cm−1, which amounts to 20% of the complete salt loss of 7.2 g s−1cm−1compiled by Katz e

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10557

年代:1986

数据来源: WILEY

摘要:

Acoustic tomography uses integrating measurements which require inverse methods to resolve the averages into estimates of spatial structure. Statistical inverse methods have been extensively used to solve the reconstruction problem over different tomographic ranges and configurations. These inverses become very difficult to apply in frontal regions like the Gulf Stream (GS) system, where the statistics are acutely inhomogeneous and anisotropic and the mean is not a likely representation of the GS front at any time. In this paper we propose an alternative inverse which asks for the solution which gives a front instead of asking for the smoothest solution. The inverse solution minimizes the errors in the fit to the data while simultaneously maximizing the sum of the squares of the gradients observed in the reconstructed section and minimizing the absolute value norm for stability. The inverse is aimed at detecting changes in the GS front, thus the data are used to estimate the perturbations to a previous estimate of the frontal structure, instead of reconstructing the entire front as a perturbation from some average state. This approach is intended to merge well with eventual dynamic updating schemes and can be used with various types of data, given a proper model. Several examples have been run intercomparing the traditional linear least squares (LLSI) with the maximum gradient inverse (MGI), from very idealized cases to a real Gulf Stream section reconstructed from hydrographic data. Different transceiver configurations were also compared and mid‐depth instruments were found to be superior to bottom mounted instruments. The simplest cases show a significant improvement in the estimate of the Gulf Stream front by the MGI compared to the weighted least squares inverse (LLSI). As the cases became more complicated (and more realistic), the differences between inverse methods become less pronounced, although the strength and location of the perturbation maxima were always determined more accurately by the MGI. The decline is at least partially due to the numerical algorithm which lumps data misfits and external constraints (the maximum gradient) into a single penalty criterion which is minimized. The most immediate way to overcome this limitation is to break up the problem into a two‐step procedure, first a least squares inverse to fit the data and second an iterative, nonlinear optimization maximizing the gradient and minimizing the absolute value n

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10566

年代:1986

数据来源: WILEY

摘要:

Moored current measurements in the Somali Current on the equator of approximately 1‐year duration reveal a seasonal cycle of the vertical current structure which is substantially different during part of the year from that previously perceived from measurements in the boundary current away from the equator. In particular, during the winter monsoon the southwestward flow at the surface reaches down only to little more than 100 m, while a northward countercurrent exists below down to 400 m. Observed current structure is quite well reproduced by a numerical model with high vertical and reasonable horizontal resolutions. Overall conclusions are that the equatorial and off‐equatorial circulation of the Somali Current are separate systems during most of the year and that remote forcing from the east along the equator appears to be a minor effect in the seasonal variability of near‐surface flow in the equatorial Somali Cu

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10581

年代:1986

数据来源: WILEY

摘要:

A newly available consolidated data set from the U.S. Navy's Fleet Numerical Weather Central in Monterey, California, is utilized to investigate global energy fluxes at the sea‐air interface. Sea surface temperature data from January 1949 to December 1979 were extracted from the data set along with air temperature, sea level pressure, dew point temperature, wind speed, wind direction, and cloud cover. Five degree latitude by five degree longitude spatial averaging and monthly temporal averaging were applied to the parameters in the data set for the purpose of studying long‐term large‐scale fluctuations. The heat balance of the global ocean surface layer is calculated using bulk flux formulations. Maps of the long‐term monthly and annual means of the net surface energy flux together with the four components of the total flux (latent heat flux, sensible heat flux, incoming radiation, and outgoing radiation) for the global oceans are presented. Incoming solar radiation and latent heat flux are the two dominant components that control net surface energy fluxes. Wind speed, cloud cover, and the gradient of specific humidity are the three most important meteorological parameters in determining surface flux. Errors associated with the bulk formula calculations and the significant features of the energy balance at the ocean surface are di

ISSN:0148-0227    

DOI:10.1029/JC091iC09p10585

年代:1986

数据来源: WILEY