摘要:

Near‐surface velocities from a shipborne acoustic Doppler instrument are used together with conductivity‐temperature‐depth and O2data to make estimates of geostrophic velocities off of Cape Hatteras. The data set consists of two transects across the Gulf Stream at approximately 73°W and 71°W made by the R/VEndeavorin August 1982. An inversion technique is applied which makes use of both the acoustic Doppler data and property conservation requirements. The method produces estimates of the absolute flow field across the two sections with formal errors of 1–2 cm/s. At the time of the observations, the net Gulf Stream transports are estimated to be 116±2×109kg/s at 73°W and 161±4×109kg/s at 71°W. A southwestward Deep Western Boundary Current transport is estimated at 4±1×109kg/s. Taken together with recent Gulf Stream transport estimates of similar accuracy made in June 1982, the results are in general larger than historical transport estimat

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02227

年代:1988

数据来源: WILEY

摘要:

A thermistor chain was towed 1400 km through the eastern North Pacific subtropical frontal zone in January 1980. The observations resolve surface layer temperature features with horizontal wavelengths of 0.2–200 km and vertical scales of 10–70 m. The dominant features, which have horizontal wavelengths of 10–100 km, amplitudes of 0.2°‐1.0°C, and random orientation, likely arise from baroclinic instability. Associated with them is a plateau below 0.1 cpkm in the horizontal temperature gradient spectrum. Strong temperature frontsO(1°–2°C/3–10 km) are observed near 33°N, 31°N, and 27°N. Temperature variability is partially density compensated by salinity, with the fraction of compensation increasing northward. There is evidence of vertical mixing during high winds. Temperature at 15‐m depth is roughly normally distributed around the climatological surface mean, with a standard deviation of approximately 0.5°C. The standard deviation would correspond to an adiabatic meridional displacement of 80–100 km in the mean gradient. Horizontal temperature gradient at 15‐m depth has maximum values in excess of 0.25°C/100 m and kurtosis near 80. In the band 0.10–1 cpkm, the 15‐m gradient spectrum is inversely proportional to wave number, consistent with predictions from geostrophic turbulence theory, while the spectrum at 70‐m depth has additional variance that is consistent with Garrett

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02237

年代:1988

数据来源: WILEY

摘要:

The Oyashio is a western boundary current of the subarctic circulation in the North Pacific. In recent years an anomalous southward intrusion of the Oyashio has been observed frequently from winter to late spring that is closely associated with the atmospheric temperature and other climatic elements of the eastern part of Japan. The anomalous southward intrusion of the Oyashio east of Japan was observed in 1963, 1974, 1981, and 1984. The average southward limit of the Oyashio water in the northern area of the Kuroshio Extension is approximately 39°–39.5°N in spring, but the Oyashio intrudes south to about 36°N in these anomalous years. The relationship between the southward intrusion of the Oyashio and the variation in wind stress over the North Pacific is examined by use of wind stress data. It has been demonstrated that prior to occurrences of the anomalous southward intrusion of the Oyashio in late spring, the southward shift of the latitude with no wind stress curl was commonly observed in the North Pacific by the development of the prominent Aleutian low. If a Sverdrup balance is assumed, the subarctic circulation shifts southward about 300–500 km from its annual mean latitude. During the Oyashio intrusion periods, stronger southeastward wind stress by the Siberian high were observed in the western region of the North Pacific, which suggests that the occurrence of the Oyashio intrusion is associated with the global change in the atmospheric circulation. However, analysis of historical data shows that if the southward shift of the wind system occurs, a warm eddy detached from the Kuroshio Extension and a large eastward expansion of the Tsugaru warm current suppress the development of the anomalous southward intrusion of the Oyashio east of Japan. A simple method to predict the anomalous intrusion of the Oyashio in late spring is proposed on the basis of these r

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02247

年代:1988

数据来源: WILEY

摘要:

Diurnal period wind stress and current fluctuations measured over the continental shelf off northern California during the Coastal Ocean Dynamics Experiment in the summers of 1981 and 1982 are examined. The diurnal currents are strongly surface intensified, with amplitudes of up to 20 cm s−1. At depths of less than 35 m, the diurnal currents are nonstationary, and their amplitude is well correlated with the amplitude modulation of the local diurnal wind stress. Beneath the surface layer, the diurnal current vectors rotate clockwise with ellipse semi‐major axes of 1 to 3 cm s−1. A mixed layer model driven with diurnal wind stress and surface heat flux produces currents similar to those observed in the upper water column. The deeper currents are consistent with the combination of a freely propagating Kelvin and first‐mode coastal‐trapped wave and, over the inner shelf, with the interior flow forced by the diurnal wind stress in the presence o

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02257

年代:1988

数据来源: WILEY

摘要:

An inverted echo sounder (IES) and deep pressure sensor were deployed within 70 km of a shallow pressure sensor at Palmyra Island (6°N, 162°W) in the central Pacific. These instruments provided yearlong records of acoustic travel time, deep pressure and sea level. Two independent time series of dynamic height are derived from travel time and sea surface elevation, respectively. The spectra of these time series are similar, and at the spectral peaks the coherence between them exceeds 99.9% confidence levels, indicating that travel time can be used to record dynamic height fluctuations. This investigation provides a frequency dependent calibration for the IES in this region. At the energetic low frequencies (periods ∼ 1 month), this calibration agrees with a calibration by the standard method using conductivity‐temperature‐depth (CTD) casts. At higher frequencies (periods of ∼3 days), using the CTD‐derived calibration may underestimate the amplitude of some processes by as

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02277

年代:1988

数据来源: WILEY

摘要:

The validation and specification of the capacity of spaceborne radar altimeters to estimate marine wind speed and ocean significant wave height are dependent upon comparisons of these quantities as estimated by radar altimeters and conventional in situ sensors mounted aboard surface buoys. Two important questions are associated with these comparisons. First, what are the expected differences between buoy and altimeter estimates of wind speed and significant wave height? Second, given a knowledge of these expected differences and a finite number of buoy‐altimeter comparisons, what conclusions can be reasonably drawn about the capacity of an altimeter to estimate wind speed and significant wave height? In this paper we outline and quantify the expected differences between buoy and altimeter estimates of wind speed and significant wave height. These differences are categorized as those associated purely with the buoy, purely with the altimeter, or the disparate manner in which buoys and altimeters sample the spatially and temporally varying wind and wave field. Based on these expected differences, statistical tests are given to validate and specify altimeter performance. In addition, statistical approaches to discriminating between candidate algorithms for converting the return pulse characteristics of a radar altimeter into wind speed estimates are discusse

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02285

年代:1988

数据来源: WILEY

摘要:

In a deployment of an ocean surface current radar system made during May 1985, currents were measured in a region of sea to the northeast of Anglesey, Wales, and compared with data obtained from three current meters. The uppermost current meter was fixed at 5 m from the surface, in a water column of 40‐m depth with tidal range of 9 m. In the east–west direction, close to the orientation of the major axis of the tidal ellipse, the radar and top current meter show good agreement to within an rms value of 0.16 m s−1, consistent with earlier comparative studies. For the weaker north–south components of the flow, however, differences between the radar results and those from the current meters are apparent. A larger‐amplitude north‐south signal is recorded by the radar. In terms of the M2rotary (clockwise and anticlockwise) components of the flow, the radar data contain amplitude and phase anomalies with respect to a predicted surface behavior deduced from the current meter records and theory. In particular, anticlockwise phase at the surface is advanced considerably (by ≃ 20°). Further analysis shows that the flow field recorded by the radar has two components: the predicted tidal response, and an additional elliptical term of lower eccentricity than the main east–west tidal signal and with major axis directed close to north. Hourly synoptic maps of tidal circulation patterns derived from the radar show a smooth transition from near‐westward flows on the ebb to near‐eastward flows on the flood. The variation of north–south residual currents with height can be interpreted in terms of a “mean state” consistent with geostrophic shear and associated with the roughly

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02303

年代:1988

数据来源: WILEY

摘要:

A one dimensional model estimation of the winter and summer mean circulation on the Argentinian continental shelf is presented. The model forcing mechanisms are surface wind stress and horizontal density gradients assuming basic Ekman dynamics. The density and wind stress field were obtained from historical data sets. The calculation predicts a northward transport of 1×106m3/s forced mainly by the wind stress, with largest values in winter. The primary density contribution is found to be from the barotropic density field. The surface velocities obtained were between 10 cm/s in summer and 17 cm/s in winter, toward the NNE. The results are consistent with both observations and other model calculations

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02311

年代:1988

数据来源: WILEY

摘要:

The 10 channels of scanning multichannel microwave radiometer data for the Arctic are examined by correlation, multiple regression, and principal component analyses. Data from April, August, and December 1979 are analyzed separately. Correlations are greater than 0.8 for all pairs of channels except some of those involving the 37‐GHz channels. Multiple regression shows a high degree of redundancy in the data; three channels can explain between 94.0 and 99.6% of the total variance. A principal component analysis of the covariance matrix shows that the first two eigenvalues contain 99.7% of the variance. Only the first two principal components contain variance due to the mixture of surface types. Three component mixtures (water, first‐year ice, and multiyear ice) can be resolved in two dimensions. The presence of other ice types, such as second‐year ice or wet ice, makes determination of ice age ambiguous in some geographic regions. Winds and surface temperature variations cause variations in the first three principal components. The confounding of these variables with mixture of surface types is a major source of error in resolving the mixture. The variance in principal components 3 through 10 is small and entirely due to variability in the pure type signatures. Determination of winds and surface temperature, as well as other variables, from this information is limited by instrument noise and presently unknown large‐scale variability in the emissivity of

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02321

年代:1988

数据来源: WILEY

摘要:

We describe observations of ambient sound beneath landfast ice in the Canadian Arctic Archipelago and interpret its evolution over the period June–August in terms of ice cracking and disintegration. The data were recorded on six bands between 50 and 14,500 Hz for the period April 2 to August 7, 1986, in Dolphin and Union Strait. The frequency dependence of the attenuation of sound in water allows separation of distant and local noise sources. In conjunction with satellite imagery and meteorological data, it is shown that strong signals in the acoustic time series are associated with major breakup events. The acoustic signal can provide predictive information about ice conditions and the approach of breaku

ISSN:0148-0227    

DOI:10.1029/JC093iC03p02333

年代:1988

数据来源: WILEY