摘要:

The flow of water from the western Pacific to the eastern Indian Ocean through the Indonesian archipelago is governed by a strong pressure gradient. Dynamic height computations determine the average sea level difference as 16 cm and show that most of the pressure gradient is contained in the upper 200 m. Sea level data from Davao in the Philippines and from Darwin in Australia are used to determine the annual signal and the interannual variations of the pressure gradient for the years 1966 to 1985. The annual signal has a maximum during the southeast monsoon in July and August and a minimum in January and February. Interannual variations are not related to the Southern Oscillation because sea level is low at both stations during El Niño events, and thus there is little influence on the sea level difference. The mechanism of the through flow is discussed, but a determination of its numerical value will have to await direct measurements. A comparison of the sea level difference with results from a numerical model by Kindle shows satisfactory agreement. It is concluded that the variability of the through flow can be monitored by sea level measurements

ISSN:0148-0227    

DOI:10.1029/JC092iC12p12941

年代:1987

数据来源: WILEY

摘要:

The seasonal variation of the physical characteristics and of large‐scale current patterns of the California Current system is examined using harmonic analysis applied to the 23 years of California Cooperative Oceanic Fisheries Investigations data collected between 1950 and 1978. The amplitude and phasing of seasonal variation in dynamic height and the overall standard deviation of dynamic height define three domains: oceanic, coastal, and an intervening transition zone. The transition zone is a broad band centered approximately 200–300 km offshore and parallel to the coast in which the seasonal range of dynamic height is a relative minimum and the standard deviation is a maximum. It is hypothesized that recurrent mesoscale eddies and energetic meanders create this zone. Such eddies and meanders would contribute heavily to the standard deviation of dynamic height but not its seasonal variation. The transition zone is coincident with the core of flow of the California Current. A strong interaction between the core of the California Current and the mesoscale eddy field is evident. Seasonal variation in the fields of temperature, salinity, σt, and oxygen is related to variations in the California Current, the Inshore Countercurrent and the California Undercurrent through vertical adjustments in the density field and through changes in transport. In the undercurrent there is an especially strong relation between seasonal variations in strength of flow and the extreme values of water mass characteris

ISSN:0148-0227    

DOI:10.1029/JC092iC12p12947

年代:1987

数据来源: WILEY

摘要:

In October–November 1983, Doppler sonars mounted on the research platformFlipwere used to scatter 75‐kHz sound from the underside of the sea surface at low angle, as well as from the interior of the mixed layer. Surface gravity waves were seen in velocity estimates from the surface scattering sonar, even though the wave conditions were unusually calm. Valid measurements of sea surface motion were obtained over the range interval 600 to 1400 m fromFlip. A second sonar which transmitted horizontally and scattered from the interior of the mixed layer also sensed surface waves, although with amplitude reduced in proportion to the decay of the motions with depth. Wave number‐frequency spectra of the observed motions are consistent with linear theory. The existence (emergence) of this technology enables the synthesis of kilometer‐long surface wave arrays in the open sea, without the cost and logistical support usually associated with large‐aperture arrays. In addition, the Doppler acoustic approach can provide information on lower‐frequency surface currents and on the spatial variations in these low‐frequency currents, such as Langmuir cells, which might affect wav

ISSN:0148-0227    

DOI:10.1029/JC092iC12p12967

年代:1987

数据来源: WILEY

摘要:

Satellite infrared observations of the Bay of Bengal during the latter part of February 1985 reveal the existence of two bands of warm water that resemble western boundary currents along the east coasts of India and Sri Lanka. A recently formed elliptical warm core eddy, with a major axis of nearly 150 km, appears at longitude 90°E and latitude 19°N at the end of the axis of the current. Color infrared images of sea surface temperature are used to illustrate the sea surface temperature patterns and to estimate their displacements with tim

ISSN:0148-0227    

DOI:10.1029/JC092iC12p12974

年代:1987

数据来源: WILEY

摘要:

Satellite photos during the summer of 1984 show the development of a band of cool water along the seaward coast of Nova Scotia during a month‐long period of upwelling favorable winds. The timing of the appearance of the cool water band, the rate at which it broadened, and the bottom‐temperature evolution at several representative points along the coast are shown to be in good agreement with an idealized two‐layer model of the wind‐driven shelf circulation. The presence of the cool water is clearly attributable to upwelling. After the temperature front moves offshore, wavelike features develop rapidly with alongshore wavelengths of 50–75 km and similar maximum cross‐shore displacement amplitudes. The associated alongshore propagation speed is at most 0.02 m s−1to the northeast. The length and time scales of these features are shown to be consistent with results from simple linear instability models which allow for both potential and kinetic energy release from the mean state by perturbations. Results suggest that the wavelike features are primarily due to baroclinic instability of the upwelling‐associated base state. Rough estimates suggest that upwelling and subsequent eddy development can play an important role in the supply of nutrients to the surface wate

ISSN:0148-0227    

DOI:10.1029/JC092iC12p12979

年代:1987

数据来源: WILEY

摘要:

Reducing the large volume of TIROS‐N series advanced very high resolution radiometer‐derived data to a practical size for application to regional physcial oceanographic studies is a formidable task. Such data exist on a global basis for January 1979 to the present at approximately 4‐km resolution (global area coverage data, ≈2 passes per day) and in selected areas at high resolution (local area coverage and high‐resolution picture transmission data, at ≈1‐km resolution) for the same period. An approach that has been successful for a number of studies off the east coast of the United States divided the processing into two procedures: preprocessing and data reduction. The preprocessing procedure can reduce the data volume per satellite pass by over 98% for full‐resolution data or by ≈84% for the lower‐resolution data while the number of passes remains unchanged. The output of the preprocessing procedure for the examples presented is a set of sea surface temperature (SST) fields of 512 × 1024 pixels covering a region of approximately 2000 × 4000 km. In the data reduction procedure the number of SST fields (beginning with one per satellite pass) is generally reduced to a number manageable from the analyst's perspective (of the order of one SST field per day). This is done in most of the applications presented by compositing the data into 1‐ or 2‐day groups. The phenomena readily addressed by such procedures are the mean position of the Gulf Stream, the envelope of Gulf Stream meandering, cold core Gulf Stream ring trajectories, statistics on diurnal warming, and the region and period of 18°C water formation. The flexibility of this approach to regional oceanographic problems will certainly extend the li

ISSN:0148-0227    

DOI:10.1029/JC092iC12p12993

年代:1987

数据来源: WILEY

摘要:

Examination of 7 years of satellite advanced very high resolution radiometer imagery demonstrates that shelf water removal by entrainment adjacent to warm‐core rings is a common phenomenon, representing an important process for shelf water budgets. South of Georges Bank, streamer entrainment occurred 69 ± 20% of the time. In addition, 9 ± 6% of the time more than one streamer was active. The data show little mean seasonal variability but large interannual variability in streamer occurrence. Most of the variability is related to the passage of warm‐core rings south of Georges Bank. An instantaneous streamer transport value of 2.5 × 105m3s−1was determined from ship‐tracked drogues and hydrographic data. Reducing this value to 70% gives an estimated mean annual shelf water removal by streamer entrainment of 1.8 × 105m3s−1(5700 km3yr−1) for this segment of the shelf. A balanced Gulf of Main transport budget can not be obtained when this value is compiled with transports across the other boundaries of the gulf; instead a net export of 16 × 104m3s−1of water results. This lack of a balance emphasizes the uncertainty of the existing transport measurements. The fate of streamers includes incorporation into the warm‐core ring and detrainment from the ring with either the formation of cold cyclonic rings in the slope water or entrainment into the northern edge of the Gulf Stream. In addition to streamer entrainment, the satellite imagery reveals that a number of different phenomena are occurring which move shelf water across the shelf‐slope front. In 86 ± 13% of the images, some type of offshor

ISSN:0148-0227    

DOI:10.1029/JC092iC12p13003

年代:1987

数据来源: WILEY

摘要:

This paper describes the use of the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) satellite data to study the ice cover in the Sea of Okhotsk during the four winters of 1978–1982. The ice concentration estimates obtained from SMMR are used to study two different polynyas: one over the Kashevarova Bank, and the other over the northwest continental shelf. For the Kashevarova polynya this study shows that the polynya, which may be related to the upwelling observed in historic summer cruises, occurs directly over the bank. For the continental shelf, which because of strong offshore winds and cold temperatures is a region of high ice production, the polynya areas are combined with heat flux estimates from weather station data to yield the production rates of ice, salt, and dense shelf water. As a previous study by Kitani (1973) shows, the mixing of this dense shelf water with Pacific water yields a water mass unique to the Okhotsk, which is the layer of cold, low‐salinity intermediate water between depths of 150 and 800 m. From our calculations, we estimate that the dense shelf water is produced at an annual rate of about 0.5 Sv, and that the intermediate water is produced at a rate of 1–2 Sv, which yields a renewal time for this layer of 10–4

ISSN:0148-0227    

DOI:10.1029/JC092iC12p13013

年代:1987

数据来源: WILEY

摘要:

A triangular array of current meter moorings was deployed within the cyclonic flank of the Gulf Stream in the South Atlantic Bight from September 1981 to April 1982. Using velocity and temperature data and the nondiffusive heat equation, a time series of vertical velocity was derived. A mean vertical velocity of −0.013 cm s−1and standard deviation of 0.078 cm s−1were obtained. To better understand the subsurface structure of Gulf Stream meanders, the time series of horizontal and vertical velocities and temperature were examined at times when events were passing through the array. The flow along the trailing edge of a Gulf Stream meander and within the leading portion of a cold core frontal eddy was found to have an upward component (positivew), while that within the trailing portion of the frontal eddy and along the leading edge of a meander had a downward component (negativew). Using the horizontal and vertical velocity time series, cross‐stream and along stream momentum balances were calculated. The downstream flow was found to be in geostrophic balance. In contrast, the Coriolis and nonlinear terms were found to contribute equally to the determination of the cross‐st

ISSN:0148-0227    

DOI:10.1029/JC092iC12p13029

年代:1987

数据来源: WILEY

摘要:

Seventeen dipole eddies, including five large, well‐formed ones, three second‐generation eddies, and two double eddies, were observed in the Alaska Coastal Current near Kayak Island in one single scene of the Landsat thematic mapper (TM) on April 22, 1985. The digital Landsat TM satellite data were computer analyzed to extract details in the near coastal circulation in the northern Gulf of Alaska. Enhancement techniques were applied to the visible and thermal IR bands. The features are evident only in the visible bands because of the ability of these bands to detect the distribution of sediments in the near surface. These eddies did not have a significant thermal signature. The sources of these sediments are the glacial streams found throughout the Gulf of Alaska coast. Eddies of this configuration and frequency have never been observed here previously. However, the oceanographic and meteorological conditions are typical for this time of year. These eddies should be important to the cross‐shelf mixing processes in the Alaska Coastal Current and are an indicator that the flow here can be unstable at certain times of the

ISSN:0148-0227    

DOI:10.1029/JC092iC12p13041

年代:1987

数据来源: WILEY