摘要:

Dissolved aluminium has been determined in sea water samples from the southwestern Alboran Sea and the Gulf of Cadiz. Partial dissolution of eolian dust is responsible for the elevated levels of dissolved Al that were found in both the Western Mediterranean Deep Water (WMDW) (111.5 nM) and Levantine Intermediate Water (LIW) (86.2 nM) masses in the Alboran Sea. The Al concentration in the outflowing plume of Mediterranean water sampled in the Gulf of Cadiz is also elevated (72 nM). These enhanced signals and the differences between them are used in a three water mass system to calculate a maximum 10% contribution of Western Mediterranean Deep Water to the outflow plume, considerably less than has been previously supposed. While the synoptic nature of this study and the possibility of involvement of other water masses in the outflow plume leave scope to increase the participation of WMDW in the outflow plume, these measurements indicate the potential of a nontransient tracer in elucidating the component parts of complex flow systems.

ISSN:0148-0227    

DOI:10.1029/JC093iC01p00591

年代:1988

数据来源: WILEY

摘要:

A methodology is presented for estimating downward longwave irradiance at the ocean surface from satellite radiance data. The downward longwave irradiance is computed with a fast and accurate radiative transfer model as a function of temperature, water vapor, ozone and carbon dioxide mixing ratios, fractional cloud coverage, emissivity of clouds, and cloud top and cloud base altitudes. A sensitivity study is performed to assess the relative importance of the model input parameters and devise strategies regarding their retrieval. Ozone and carbon dioxide mixing ratios are consequently fixed at their climatological values, whereas the other parameters, highly variable in space and time, are determined from satellite data. Temperature and water vapor mixing ratio are obtained from NOAA Tiros operational vertical sounder data, and cloud parameters are retrieved from GOES visible and infrared spin scan radiometer data. Several methods are investigated to retrieve the cloud parameters. In the most refined method, cloud base altitude is deduced from cloud top altitude and liquid water path, assuming a vertical liquid water distribution within the clouds. In the other methods, simplifying assumptions are introduced, which include directly relating liquid water path to cloud geometrical thickness, fixing the cloud geometrical thickness to its climatological value, and, finally, parameterizing the cloud effects only as a function of fractional cloud coverage. Satellite‐derived irradiances are compared to those measured in situ during the Mixed Layer Dynamic Experiment, conducted in October–November 1983 off the central California coast. The results indicate that the satellite methods perform similarly, with standard errors of estimate ranging from 21 to 27 W m−2on a half‐hourly time scale and from 16 to 22 W m−2on a daily time scale. These errors correspond to 6 to 8% and 4 to 6% of the average measured values, respectively. When compared with techniques based on empirical formulas that employ conventional surface data, the satellite methods also exhibit similar standard errors of estimate. The satellite methods, however, are favored, since they are generally less biased and globally a

ISSN:0148-0227    

DOI:10.1029/JC093iC01p00597

年代:1988

数据来源: WILEY

摘要:

The mechanisms that control low‐frequency acoustic propagation and that are unique to the shallow water environment are resident in the seabed. A method of determining the sediment attenuation of low‐frequency compressional waves as a function of frequency and sediment depth is examined. The method utilizes the Backus‐Gilbert geophysical inverse theory, and the emphasis is placed on assessing the resolution and error associated with the inferred structure and the experimental geometry, rather than merely obtaining a solution that fits the simulated data. A laterally homogeneous geoacoustic test model is used to generate artificial data for input to the inverse procedures. The results provide insights regarding resolution and error for generically similar sediments and experimental geome

ISSN:0148-0227    

DOI:10.1029/JC093iC01p00621

年代:1988

数据来源: WILEY

摘要:

An analysis of satellite data collected over a period of 9 years as well as historic hydrographic data show that the northern Agulhas Current is subject to large, intermittent, and solitary meanders. These transient events, collectively named the Natal pulse, progress downstream at consistent rates of 21 cm/s. Upon reaching the area where the shelf broadens, their rate of progression slackens to 5 cm/s. They are present in some stages of development at least 17% of the time, extend offshore by about 170 km on average, and show a continuous lateral growth on moving downstream. With few exceptions the pulses are spawned as cold core, cyclonic, trapped lee eddies in the Natal Bight. They are held responsible for the intermittent coastal counter currents observed inshore of the Agulhas Current along the southern African coast and may play a crucial role in sediment distribution on the shelf.

ISSN:0148-0227    

DOI:10.1029/JC093iC01p00631

年代:1988

数据来源: WILEY

摘要:

Aerial survey results are presented which show a modification of the lower atmosphere on crossing the edge of the Agulhas Current near 37°S, 20°E. Profiles of air temperature and dewpoint show increases in marine boundary layer heights of about 400 m as sea surface temperatures rise suddenly from 18° to 24°C. Westerly winds increase across the NE‐SW aligned sea surface temperature front by 7 m s−1, in a sea breeze‐like circulation. Surface latent and sensible heat fluxes to the atmosphere change from 100 W m−2to 340 W m−2on entering the Agulhas Current because of feedback processes between warmer sea surface temperatures, turbulence, and wind stress. The data sample is small and statistically limited, but the case study results indicate that the response of the lower atmosphere to the Agulhas Current is similar to that found over the Gulf Stream and other warm western boun

ISSN:0148-0227    

DOI:10.1029/JC093iC01p00647

年代:1988

数据来源: WILEY

摘要:

The spectral analysis of unequally spaced data is discussed with reference to two examples of vertical profiles of internal wave displacement. For our examples, a Conductivity, Temperature, Depth probe was used to record temperature from which the wave displacements were determined. Ship heave, among other causes, resulted in the data being recorded at unequal intervals of depth. Spectral analysis is complicated by unequal data spacing, but the necessity of using an appropriate method is demonstrated by the comparison of results from two such methods with those from two analyses based on equispaced techniques. The equispaced analyses produce results consistent with the currently accepted picture of internal wave spectra but not with the results from the analyses which take account of the unequal spacing. This has important ramifications for Oceanographic spectral analysis procedure. It is clear from our examples that the variability inherent in the unequal spacing has a much greater effect than one might at first imagine. In particular, our examples suggest that important structure at higher wave numbers may be totally lost if inappropriate methods of analysis are used.

ISSN:0148-0227    

DOI:10.1029/JC093iC01p00655

年代:1988

数据来源: WILEY