摘要:

Results of impulse radar, ice crystalcaxis, and subice current measurements on the fast ice near Narwhal Island, Alaska, are presented. The crystal structure of the ice was found to have a horizontal crystalcaxis with a preferred azimuthal orientation. This orientation was found to align with the direction of the current at the ice‐water interface. Impulse radar reflection measurements revealed that the preferred orientation of the sea ice crystal structure behaved as a microwave polarizer. It was observed that when the antennaEfield was oriented parallel with thecaxis of the crystal platelets, a strong reflection of the radar signal from the bottom of the ice was obtained. However, when the antennaEfield was oriented perpendicular to thecaxis, no bottom reflection was detected. The results of this study fully support earlier reports of sea ice inhomogeneity and anisotropy in reference to both structure and electromagnetic energy transmissio

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06037

年代:1978

数据来源: WILEY

摘要:

Subsurface current data from a 2‐week period in August and September 1977 are compared with coastal wind stress and water level data to describe longshore motion in reponse to the passage of Hurricane Anita across the northern Gulf of Mexico. Current meters 2 and 10 m above the bottom 21.5 km off the central Texas Gulf coast indicate strongest speeds of approximately 70 and 80 cm/s, respectively, coinciding closely with the time of maximum wind stress. A qualitative comparison of the variations in sea surface slope and wind stress with the recorded longshore current suggests that both wind stress and the longshore pressure gradient combined to produce the strong flow recorded during the storm but that the pressure gradient was primarily responsible for decelerating the current after the storm made landfal

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06047

年代:1978

数据来源: WILEY

摘要:

Prototype instrumentation designed to measure light scattering and transmission and the horizontal components of fluid velocity at a point 100 cm off the sea floor was deployed on the Long Island inner shelf for a 27‐day period in October and November of 1976. Depth at the point of deployment was 10.5 m. Data were taken from sensors in hourly bursts consisting of 468 consecutive 1‐s samples. Measurements taken with the electromagnetic current sensor were converted to absolute units by using a laboratory calibration, while absolute calibration of the turbidimeter in terms of suspended matter concentration was accomplished by using a combination of laboratory and field measurements. The results from the deployment show the effects of water motions at both wave and subtidal frequencies on sediment concentrations. Although burst mean fluid motions during the observation interval were primarily of tidal frequency, a single wind‐forced event caused burst mean currents in excess of 38 cm/s. During that same event, suspended particulate concentrations rose to a burst mean of 79 mg/l from a prestorm level of 5 mg/l, an order of magnitude increase occurring over a period of approximately 12 hours. During the storm event, individual burst records show that fluid motions at surface wave frequencies and with amplitudes of over 100 cm/s occurred at the experimental site. The near‐bottom suspended matter field at that time was found to have appreciable energy at surface wave frequencies as well. Changes in suspended matter concentration of the order of 130 mg/l were observed to occur in a period of 3–5 s. Increased burst mean concentration was seen to accompany increased wave activity, although increased mean flow with declining wave activity also led to increased suspended particulate concentration. When storm conditions (wave activity and mean flow much above deployment interval ambients) abated, concentrations returned to ambient levels in approximately 12 hours. Coherence between suspended matter concentration and horizontal fluid velocity was found to be statistically significant during four intervals of the deployment. In most cases the significance was centered around a broad frequency band near 0.1 Hz. Vertical near‐bottom wave velocities were inferred from the current measurements. The analysis of coherence and phase between the vertical velocity and concentration supports the hypothesis that part of the measured concentration signal was due to the vertical oscillatory advection of the mean concentration field past the turbidimeter during the passage of su

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06052

年代:1978

数据来源: WILEY

摘要:

Two analytic models are developed to describe rip current cells on an open coastline with sloping planar foreshore and flat offshore bathymetry. Both models extend the work of LeBlond and Tang (1974) to include the refraction of the normally incident wave field by the nearshore circulation. The first model includes the effect of the currents on the incident wavelength, but no change in wave direction, and shows that no rip currents are possible. The second, more complete model considers the refraction of the waves as well and predicts rip current cells. The spacing of the rip currents and their associated variables are shown to be a function of one dimensionless parameter. Comparison of the predicted spacing with some published field data as well as with measurements obtained on the Isle of Sylt, West Germany, shows reasonable agreement with the second model.

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06063

年代:1978

数据来源: WILEY

摘要:

Drawing from wind and current meter data, an empirical, semiquantitative model has been developed for wind‐induced current flow in the New York Bight apex portion of the Hudson Shelf Valley. Data have shown that winds from 270°T (±50°), blowing for at least 9 hours at speeds of greater than 5 m/s, can cause northward (upchannel) bottom flow in the shelf valley at velocities in excess of 40 cm/s. Southern (downchannel) flow is initiated by winds from 75°T (±35°) blowing for at least 6 hours at speeds of 4 m/s or more. Seasonal variation in the wind field results in predominant upchannel flow during October–April with downchannel flow throughout the rest of

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06073

年代:1978

数据来源: WILEY

摘要:

In 1976 and 1977 current measurements were made on the Peru continental shelf and slope as part of the Coastal Upwelling Ecosystems Analysis expedition Joint II. The fluctuations in current were not well correlated with the local wind, in contrast to observations from coastal upwelling regions off Oregon and northwest Africa. Data from current meter arrays at separations up to 700 km are available for periods of 40–75 days. Subtidal (0.05–0.25 cpd) fluctuations propagate coherently at 200 km d−1in a poleward direction. Analysis of current, water temperature, and sea level time series suggests that these fluctuations have an offshore scale of 70 km and represent baroclinic Kelvin waves, whose origin is equatorward of 10°S and which propagate to at leas

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06083

年代:1978

数据来源: WILEY

摘要:

An intensive three‐dimensional survey of the Antarctic Polar Front was made in the Drake Passage in March 1976. The front, which was imbedded within one of the high‐velocity cores of the circumpolar current, is viewed as a water mass boundary demarking the northern extent of near‐surface antarctic waters. Within the front, water masses are observed to intrude, one above the other, with characteristic vertical scales of 50–100 m. The intrusions are horizontally anisotropic, being elongated in the alongstream direction and constrained primarily to the upper 800 m of the front. The spatial and temporal persistence of the variability is examined through the analysis of continuous vertical profiles of horizontal velocity, temperature, salinity, and oxygen with discrete sampling of nutrients. Analysis of the velocity data showed the mean current flowing to the NNE with speeds of the order of 30–40 cm s−1in the upper 600 m, with temporal variability over a 28‐hour ‘yo‐yo’ due primarily to internal gravity waves. The thermohaline variability was not internal wave induced but rather was associated with nearly isentropic advection of different water masses across the front. Cold fresh and warm salty intrusions did not conserve potential density, however, and double‐diffusive transfers are strongly suggested as being crucial to an understanding of the dynamics of the intrusions. Applying a model (Joyce, 1977) for lateral mixing we estimate poleward temperature and salinity fluxes due to interleaving of 0.086°C cm s−1and 0.069‰ cm s−1, respectively. If these values are typical, interleaving could play a significant role in large‐scale balance of salt and, to a lesser exten

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06093

年代:1978

数据来源: WILEY

摘要:

Analyses of hydrographic data from a single winter cruise and of 29 years of climatological surface temperature data are used to describe some horizontal and vertical properties (and their interrelations) of a large‐scale longitudinal temperature maximum in the eastern North Pacific. The climatological surface temperature data for individual monthly means at 35° and 40°N from 1947 to 1975 show that (1) the position of the permanent large‐scale temperature maximum at 35°N in the eastern Pacific almost always lies to the west of that of the corresponding maximum at 40°N, and the average angle counterclockwise from the east of the line connecting the two maxima is about 40° and (2) a positive correlation exists between the temperature and east‐west scales of the longitudinal temperature variation at 40°N. Both results agree with preliminary analyses based on long‐term averages of monthly mean temperatures (Kenyon, 1977a). The hydrographic data from March and April 1976 along 35°N show that both the depth scale and the east‐west scale associated with the temperature maximum in the eastern Pacific can be related to the surface layer thickness and are about 100 m and 4000 km, respectively. The surface layer thickness, defined by a temperature‐salinity relation, is relatively large (small) when the surface temperature is relatively high (low), a relation which holds for the large‐scale horizontal variability in the eastern Pacific as well as for the smaller‐scale (500 km) variability in the western Pacific. The hydrographic data at 35°N show also that the maximum surface temperature in the eastern Pacific is significantly west of the maximum surface layer thickness. Beneath the maximum surface layer temperature, where the vertical temperature gradient is large, the isotherms slope downward from west to east. The geostrophic surface velocity relative to 250 dbar, where the isotherms are nearly level, has a northward component in a broad region surrounding the surface temperature maximum. The hydrographic data strengthen the interpretation that the longitudinal surface temperature maximum is predominantly associated with horizontal advection in the surface layer, which has a significant northward component, and is the surface expression of a mechanism of net poleward heat transport

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06115

年代:1978

数据来源: WILEY

摘要:

The infrared capabilities of the Geostationary Operational Environmental Satellite (Goes) are analyzed to obtain multiyear time histories of Gulf Stream meanders. Radiative transfer calculations using monthly mean profiles of atmospheric temperature and moisture are shown to overestimate cloud‐free equivalent soundings by 2–5 K. A simple relation is derived between temperature at the satellite, sea surface temperature, and transmissivity of the atmosphere at 11.6 μm, which allows an observer to determine if a known sea surface temperature gradient is observable from Goes knowing only the precipitable water content along the slant path to the spacecraft. More than 2 years of Goes observations of Gulf Stream meanders are analyzed as a randomly spaced time series using least squares spectral analysis; the dominant periods in the spectra, based on 1976–1978 data, are 250,65, and 10 days in the Gulf of Mexico; 30 and 6 days off Onslow Bay, North Carolina; and 45 and 5 days off New England. A summary of the meanders between the Yucatan Strait and the Grand Banks shows that the largest latitudinal variability is associated with the Gulf Loop Current. Comparison of meander periods with least squares spectra of historical Florida Current transports suggests that meanders in the Gulf of Mexico are related to variability with 4‐ to 16‐day and 40‐ to 100‐day perio

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06123

年代:1978

数据来源: WILEY

摘要:

During 1975 several shipboard expendable bathythermograph surveys plus satellite infrared imagery provided a nearly synoptic view of the distribution and number of Gulf Stream rings in the western North Atlantic. Twelve rings were identified; nine were cyclonic (cold core) rings and three were anticyclonic (warm core) rings. This is the largest number of rings ever observed during a short period of time (4months). Evidence suggests that the mean movement of these rings was southwestward.

ISSN:0148-0227    

DOI:10.1029/JC083iC12p06136

年代:1978

数据来源: WILEY