摘要:

Warm‐core ring (WCR) 83D passed through a linear array of moored temperature, conductivity and velocity sensors during October 1983. Satellite‐derived thermal imagery combined with data from the moored sensors have revealed a cold‐core cyclonic eddy, of approximately 80‐km diameter, traveling in advance of ring 83D. This cyclone, whose angular momentum magnitude was about 1/3 that of the WCR, evolved either during or shortly after the WCR's formation. Hydrographic and moored sensor data suggest that the WCR brought about a subsurface exchange of shelf and slope water, with near‐surface slope water moving onshore and near‐bottom shelf water being drawn offshore and around the ring. Examination of 308 cross‐shelf hydrographic sections from the Middle Atlantic Bight has indicated that such exchange commonly occurs in the presence of a WCR. This apparent ring‐induced exchange may significantly affect the overall salt balance of Middle Atlantic Bight shelf water. As an example, the volume of slope water within a well‐surveyed intrusion, which lay onshelf of WCR 79B, was 16% of Wright's (1976) estimate of the annual slope water transport to the Middle Atl

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09615

年代:1986

数据来源: WILEY

摘要:

Our earliest intercomparisons between western North Atlantic data and eddy‐resolving two‐layer quasi‐geostrophic symmetric‐double‐gyre steady wind‐forced numerical model results focused on the amplitudes and largest horizontal scales in patterns of eddy kinetic energy, primarily abyssal. Here, intercomparisons are extended to recent eight‐layer model runs and new data which allow expansion of the investigation to the Kuroshio Extension and throughout much of the water column. Two numerical experiments are shown to have realistic zonal, vertical, and temporal eddy scales in the vicinity of the Kuroshio Extension in one case and the Gulf Stream in the other. Model zonal mean speeds are larger than observed, but vertical shears are in general agreement with the data. A longitudinal displacement between the maximum intensity in surface and abyssal eddy fields as observed for the North Atlantic is not found in the model results. The numerical simulations examined are highly idealized, notably with respect to basin shape, topography, wind‐forcing, and of course dissipation. Therefore the zero‐order agreement between modeled and observed basic characteristics of mid‐latitude jets and their associated eddy fields suggests that such properties are predominantly determined by the physical mechanisms which dominate the models, where the fluctuations are the result of instability processes. The comparatively high vertical resolution of the model is needed to compare with new higher‐resolution data as well as for dynamical reasons, although the precise number of layers required either kinematically or dynamically (or numerically) has not been determined; we estimate four to six when no attempt is made to account for bottom‐ or near‐surf

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09624

年代:1986

数据来源: WILEY

摘要:

The inverse method of Wunsch (1978) for determining steady state ocean circulation patterns is examined using a numerical model as the source of both data and observations. A simple, but commonly used, formulation of the technique is tested. The studies carried out have relevance to other descriptions, as they focus on features common to all formulations. The theme of the paper is a study of present methods rather than a comprehensive survey of parameter space. It is found that an optimizing principle of least perturbation from an initial velocity field can produce flows that are highly correlated with the observed fields. This is when station spacing is of the order of 1° – 2° and the number of layers is not greater than the number of vertical observations. Allowing flow through all faces of the boxes gives significantly more realistic velocities than merely having horizontal flow. However, three major problems arise with the box method. These are the inability to handle significant shears with moderate sampling, the lack of a uniformly successful way to decide on an initial state, and the necessity of using boxes of limited size. In particular, when the method uses boxes straddling an entire basin, the results are p

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09639

年代:1986

数据来源: WILEY

摘要:

Analyses of wind, adjusted sea level, temperature, salinity, and current data show that the Alaska Coastal Current (ACC) flows generally westward from Shelikof Strait to the Shumagin Islands. The seasonal nature of the ACC in the western Gulf of Alaska is similar to that in the northern gulf, but minimum salinity, maximum current speeds, and changes in baroclinic transport are less extreme to the west. Southwest of Shelikof Strait the ACC apparently is bifurcated by the bathymetry. One branch continues flowing along the Alaska Peninsula, and the other flows south. The southward flowing branch may rejoin the westward flowing one in the sea valley just east of the Shumagin Islands.

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09655

年代:1986

数据来源: WILEY

摘要:

The radiative and physical characteristics of the Weddell Sea ice cover and its marginal ice zone are studied using multichannel satellite passive microwave data in conjunction with in situ observations during the 1983 Antarctic Marine Ecosystem Research at the Ice Edge Zone Experiment. Time series studies from winter through spring, using every other day observations from the Nimbus 7 scanning multichannel microwave radiometer, reveal significant spatial variability of the brightness temperatures of consolidated ice in winter and a recurring temporal and oftentimes larger spatial variability in spring. The recurring effect in spring was found to be strongly correlated with observed surface air temperatures and is apparently associated with the cyclic changes in wetness of the snow cover of the ice while experiencing the freeze‐thaw cycle. Analysis of scatter plots of observed brightness temperatures from selected study regions using two or three frequencies and/or polarizations shows that to effectively discriminate ice from open water within the ice pack, a minimum of two channels at different frequencies, preferably 18 GHz and 37 GHz, is required. Serious problems associated with using only one frequency, even at two polarizations, (i.e., 37 GHz, and perhaps higher frequencies) have been observed. Ice concentrations derived from the sensor are compared with helicopter and ship observations, and results show consistency but a relatively low correlation coefficient partly due to the quasi‐qualitative nature of the in situ observations and uncertainties in ice emissivity in spring. The character and the northernmost extent of the ice margin are quantified using radial plots of ice concentration across the ice pack and into ice free ocean. Temporal changes in the ice margin structure are compared with ship data of physical temperature, ice characteristics, wind, and weather. Studies of the mass balance of fresh water and of biological features of the marginal ice zone are shown to benefit from time series information concerning the position of the ice edge as derived from satellite remote sens

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09663

年代:1986

数据来源: WILEY

摘要:

Statistical models for the seasonal prediction of iceberg severity in the Labrador Sea are developed from observational data for the years 1955–1984. The predictors are the monthly fields of sea level pressure and 700‐mbar geopotential height over the region north of 15°N. The primary statistical tools are gridded correlation patterns and multiple regression. Statistical significance is established by Monte Carlo simulations of the experimental procedure and by the use of a “jackknife” procedure for testing on independent data. Associations are found between iceberg severity and the circulation fields of the antecedent winter and spring. At lead times of 3–6 months, the mean absolute errors in the long‐range forecasts of severity rank are approximately 4–5 (6–7) ranks in dependent (independent) samples of 30 years. These errors are significantly smaller than the corresponding chance level value of 9.6 (± σ = 1.2). The spatial patterns depicted by the predictor fields are dominated by the North Atlantic Oscillation and are synoptically compatible with eastern Canadian iceberg conditions in both ex

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09683

年代:1986

数据来源: WILEY

摘要:

A multibeam microwave radar altimeter concept is numerically simulated to evaluate its capability to remotely sense mesoscale oceanographic features and eddies in particular. The study tests the sensitivity of the sensor to variations of systematic and environmental parameters, including sensor attitude angle, sensor position, and system errors. A novel concept of computing eddy vorticity from the multibeam data is explored. Application of this concept to the detection of simulated ocean eddies in the presence of tracker noise gives excellent results; the technique is shown to be simple and accurate. The minimum size of the eddy detectable by the multibeam altimeter is presented for a given performance characteristic of the radar.

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09693

年代:1986

数据来源: WILEY

摘要:

The ocean wave‐radar modulation transfer function (MTF) at 35 GHz (Kaband) was measured with a coherent pulsed Doppler scatterometer from a research platform in the North Sea. The Bragg waves corresponding to this radar freqency at intermediate incidence angles are capillary waves with a wavelength of about 0.5 cm. During the experiment the air‐sea temperature varied between −1°C and −5°C, which implies that the boundary layer at the air‐sea interface was unstable. The measurements at 35 GHz yield the following results: The modulus of the dimensionless MTF decreases with increasing wind speed and is larger for horizontal (HH) than for vertical (VV) polarization. The value of the dimensionless MTF for HH polarization varies between 3.5 and 9.5 in the frequency range between 0.11 and 0.14 Hz, and that for VV polarization varies between 2.5 and 7.5 depending on wind speed. The phase of the MTF for HH polarization is such that the maximum of the radar return originates from the leeward (forward) face of the long ocean waves between 0° and 15° away from the wave crests. The phase of MTF for VV polarization lies between −75° and −30°, which means that the maximum of the radar return originates from the windward (rear) face of the long ocean waves. We conclude that the phase dependence of theKaband MTF implies that the maximum of the hydrodynamic modulation for these capillary waves occurs at the windward face of the long ocean waves. The nonuniform distribution of the 0.5‐cm waves with respect to the long ocean wave profile is probably caused by a wave‐induced spat

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09701

年代:1986

数据来源: WILEY

摘要:

A statistical description of the deep ocean internal wave field is presented using measurements from the Midocean Acoustic Transmission Experiment, conducted near Cobb Seamount in the NE Pacific (46°46′N, 130°47′W) during June–July 1977. The unique feature of this experiment is the variety of data obtained simultaneously from the same location: time series of temperature and velocity, and vertical and horizontal profiles of temperature. A generalized form of the Garrett‐Munk (GM) internal wave spectrum is developed and used to interpret the data. This spectral model is specified by three parameters,E˜,t, andp(energy level, wave number bandwidth, and frequency spectral slope, respectively). The variety of measurement types permit these three model parameters to be estimated from more than one measurement. The overall best fit values to the MATE data werep= 2.7 (GM usep= 3),t= 3.1 m−1s (equivalent toj*= 6, twice the GM value), andE˜=8×10−4 j/kg(within 20% of the GM level). Although significant differences were found in the values of the bandwidth (t) and spectral slope (p) from those specified by Garrett‐Munk, the deviations are consistent with the behavior expected in a random

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09709

年代:1986

数据来源: WILEY

摘要:

This paper seeks to answer the question, How much of the internal tide propagating up Knight Inlet, British Columbia, is reflected by a right‐angled bend? The internal tide in Knight Inlet is generated by the interaction of the barotropic tide with a shallow sill seaward of the bend. It then propagates in both directions as a traveling Kelvin wave. The up‐inlet propagating wave then encounters the bend, where some of it may be reflected. The study is based upon 2⅓ months of cyclesonde current meter data from four stations taken during the summers of 1981 and 1983. The vertical profiles of amplitude and phase of theM2constituent of longitudinal velocity and density fluctuations are decomposed into a truncated series of normal modes for waves propagating both up‐inlet and down‐inlet. At the two stations up‐inlet of the sill, acceptable fits can be obtained using only two up‐inlet propagating waves, indicating that the data are compatible with the low reflection found by Webb and Pond (1986). At the two stations seaward of the sill, the up‐inlet energy flux is of the same order of magnitude as the down‐inlet flux, indicating a second source of internal tide seaward of those two stations. The results indicate that only 30–50% of the power removed from the barotropic tide is being fed into the internal

ISSN:0148-0227    

DOI:10.1029/JC091iC08p09721

年代:1986

数据来源: WILEY