摘要:

For a significant range of offshore wave conditions and foreshore slopes, run‐up observations are compared to semiempirical formulations and predictions of an existing numerical model based on the depth‐averaged one‐dimensional nonlinear shallow water equations with bore‐like breaking wave dissipation and quadratic bottom friction. The numerical model is initialized with time series of sea surface elevation and cross‐shore velocity observed in 80 cm mean water depth (approximately 50 m offshore of the mean shoreline) on a gently sloping beach and in 175 cm water depth (100 m offshore of the shoreline) on a steep concave beach. Run‐up was measured with a stack of resistance wires at elevations 5, 10, 15, 20, and 25 cm above and parallel to the beach face. At sea swell frequencies (nominally 0.05

ISSN:0148-0227    

DOI:10.1029/96JC02432

年代:1996

数据来源: WILEY

摘要:

Sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches (a steep concave‐up beach, a gently sloped approximately planar beach, and a beach with an approximately flat terrace adjacent to a steep foreshore) were depth limited (i.e., approximately independent of the offshore wave height), consistent with previous observations. The wave evolution is well predicted by a numerical model based on the one‐dimensional nonlinear shallow water equations with bore dissipation. The model is initialized with the time series of sea surface elevation and cross‐shore current observed at the most offshore sensors (located about 50 to 120 m from the mean shoreline in mean water depths 0.80 to 2.10 m). The model accurately predicts the cross‐shore variation of energy at both infragravity (nominally 0.004

ISSN:0148-0227    

DOI:10.1029/96JC02433

年代:1996

数据来源: WILEY

摘要:

A coupled ocean‐atmosphere model is used to investigate the equatorial Indian and Pacific Oceans' response to the seasonally varying monsoon winds and the relationship between monsoon variations and the El Niño‐Southern Oscillation phenomenon (ENSO). The atmosphere is a simple linear shallow water system driven by a mass source/sink term that is proportional to the sea surface temperature (SST) over the oceans and the heat balance over land. The ocean is modeled using theAnderson and McCreary[1985] reduced‐gravity transport model driven by atmospheric wind stress forcing and a parameterized heat flux. The model domain includes both the Indian and Pacific Oceans and land masses to represent Asia and Africa. Results show that variations in the model's monsoon circulation (evolving somehow from other influences) induce changes in the large‐scale circulation associated to ENSO. In this way the year‐to‐year differences in the monsoon impact on the longer‐period, coupled ocean‐atmosphere dynamics of the near‐equatorial Pacific basin. By changing the amplitude of the monsoon forcing the interval between ENSO‐like warm events varies, while the variability in the annual cycle over the Indian Ocea

ISSN:0148-0227    

DOI:10.1029/96JC00670

年代:1996

数据来源: WILEY

摘要:

An atmospheric surface forcing data set with synoptic temporal resolution is constructed for the U.S. Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time Series (BATS) site for 1988–1992. The forcing data set is based primarily on the 6‐hourly European Centre for Medium Range Weather Forecasts (ECMWF) operational analysis, daily cloud fraction and surface insolation estimates from the International Satellite Cloud Climatology Project, and monthly derived satellite precipitation estimates from the microwave sounding unit. Good agreement is found between the ECMWF surface properties (e.g., wind speed, air temperature) and synoptic meteorological data from the Bermuda airport and Comprehensive Ocean‐Atmosphere Data Set (COADS) ship reports, though the analysis tends to damp the amplitude of extreme weather events. Monthly air‐sea heat and freshwater flux estimates are generally consistent with climatological estimates for the BATS region. The diagnosed net heat and freshwater fluxes from the BATS conductivity‐temperature‐depth data show significant additional month to month variability that is not related to local atmospheric forcing but appears to arise from mesoscale advection. The surface forcing data set is then coupled to a one‐dimensional upper ocean boundary layer model, and the resulting simulations quantitatively reproduce much of the observed behavior of sea surface temperature, heat content, and mixed layer depth for the BATS site for the period October 1988 through September 1992. The induced variability in the ocean model on diurnal and storm timescales is analyzed, and the impact of using the ECMWF analysis data rather than synoptic ship or mooring observations is also examined. The main deficiencies in the simulation are related to the influence of advective events in the BATS record and to possible shifts in the ECMWF model, and preliminary techniques for addressing these problems by incorporating the horizontal advective effects are presented. The difficulties associated with directly verifying local one‐dimensional models using coarsely sampled time‐series data

ISSN:0148-0227    

DOI:10.1029/96JC01424

年代:1996

数据来源: WILEY

摘要:

An one‐dimensional differential model of the vertical structure of the turbulent active layer of the sea based on the theory of the rotationally anisotropic turbulence is proposed. The present article consists of two parts. The first part gives the definition of the class of rotationally anisotropic turbulence (RAT) and presents the basics of the theory of RAT. In the second part the theory is used to describe the evolution of the vertical structure of the turbulent active layer of the ocean within the framework of the traditional model assumption about the horizontal homogeneity of all the fields under consideration. A set of submodels (including the analogue to the classical mixing length model) is derived and discussed. The model is used under different initial and boundary conditions. Depending on the actual conditions the model describes various effects: the appearance of the upper mixed layer with a steep thermocline below it, the switching between the convective and diffusive mixing regimes, the staircase‐like structure of the thermocline (caused by unsteady shear flow or by double‐diffusion instabilities), and the modulation of the velocity field by the period of the oscillation of the heat flux. The set of the model coefficients is determined on the basis of sea surface temperature data from the ocean weather station (OWS) Papa. The results of the following computations of temperature distribution show a reasonable similarity between the model results and the corresponding data from the OWS Papa and the Long‐Term Upper Ocean Study

ISSN:0148-0227    

DOI:10.1029/96JC01988

年代:1996

数据来源: WILEY

摘要:

We present a straightforward method for estimating surface circulation on anfplane from a set of irregularly spaced vertical density profiles. The first step is to express bottom density ρhas the sum of a meanρ˜hfor a given water depthhand an anomaly,ρ′h=ρh−ρ˜h. Sea level η can then be decomposed into a dynamic heightη˜relative to a deep reference level and a correction term,η′=η−η˜. The dynamic height is estimated using a generalization of the method ofHelland‐Hansen[1934] for diagnosing flow through a cross‐shelf section under the assumption of zero bottom geostrophic flow. The correction η′ satisfies a two‐dimensional elliptic partial differential equation forced by the bottom density anomaly, wind stress and the open boundary conditions. Before calculating the density‐driven component of η′ we first test if the ρ′hare statistically different from uncorrelated noise. If they are not, the correction associated with the bottom density anomaly is set to zero. Thus the method has a degree of robustness to errors in the density observations. If the ρ′hhave well‐defined spatial structure the elliptic equation is solved for η′ and sea level is equated toη˜+η′. Note that even if this last step is required the only gridding of the density data is two‐dimensional. This makes the proposed method simpler to use than many of the existing diagnostic models which require a three‐dimensional gridding of the observed density profiles. To test the method, we use it to diagnose the flow from an idealized density field overlying an isolated topographic feature. The predicted sea level and flow fields are then compared, and shown to be in good agreement, with results from the Princeton Ocean Model. The method is then used to diagnose the winter surface circulation on the Scotian Shelf from observed density profiles. The reliability of the diagnosed flow pattern is assessed by comparing it against all available near‐surface current measurements. The differences between the observed and diagnosed currents are used to estimate the remotely forced circulation on the Scotian Shelf. It is shown that the main features of the circulation can be explained by gradients in the density field. Remote forcing is important near the coast and the

ISSN:0148-0227    

DOI:10.1029/96JC01331

年代:1996

数据来源: WILEY

摘要:

High spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the James River estuary, Virginia, during the first few hours of flood. The current measurements were made with a surface‐towed acoustic Doppler current profiler which was used in both profile and side‐scan configurations. The profile data show a 30–50 cm s−1inflow of water from the Chesapeake Bay, a time‐evolving across‐front density gradient, and downward velocity beneath the front of about 15 cm s−1. The side‐scan observations directly measure the across‐front change in current and provide a view of the three‐dimensional character of the frontal interface. The near‐surface horizontal strain rate, a critical parameter for understanding the modulation of surface waves across the front, is estimated to be about 0.04 s−1. UsingPhillips' [1984] theory as a guide, fronts with such large strain rates as these should be discernible in imagery from the ERS 1 C band synthetic aperture radar for

ISSN:0148-0227    

DOI:10.1029/96JC02384

年代:1996

数据来源: WILEY

摘要:

The circulation and particle transport through a narrow inlet (Kelvin number<0.5) and onto a sloping shelf are numerically examined using a three‐dimensional hydrodynamic model. The model domain consists of an estuarine basin with vertical density stratification separated from a well‐mixed sloping shelf by a narrow inlet. Forcing is supplied by semidiurnal tides and buoyancy differential. Strong ebb flows resulting from this combined forcing transport estuarine water seaward through the inlet to form a radially spreading buoyant surface plume over the shelf. A series of radial density fronts corresponding with the ebbing tidal outflow are found on the seaward side of the inlet mouth and are convergence zones for floating particles. Strong anticyclonic frontal flow advects particles around the boundary of the outflow plume. Particles released nearest the seaward side of the inlet mouth are able to enter the inlet at depth and remain, while those particles released farther offshore rarely enter the inlet. This result has clear implications for the shelf‐to‐estuary transport of pollutants or the larval phase of marine species. Asymmetric tidally induced eddies which appear on both sides of the inlet also contribute to the near‐field circulation. Calculations of gradient Richardson number in the inlet show that regions susceptible to enhanced mixing occur during periods of maximum tidal velocities due to increa

ISSN:0148-0227    

DOI:10.1029/96JC02529

年代:1996

数据来源: WILEY

摘要:

Mobile Bay is a wide (25–50 km), shallow (3 m), highly stratified estuary on the Gulf coast of the United States. In May 1991 a series of instruments that measure near‐surface and near‐bed current, temperature, salinity, and middepth pressure were deployed for a year‐long study of the bay. A full set of measurements were obtained at one site in the lower bay; all but current measurements were obtained at a midbay site. These observations show that the subtidal currents in the lower bay are highly sheared, despite the shallow depth of the estuary. The sheared flow patterns are partly caused by differential forcing from wind stress and river discharge. Two wind‐driven flow patterns actually exist in lower Mobile Bay. A barotropic response develops when the difference between near‐surface and near‐bottom salinity is less than 5 parts per thousand. For stronger salinity gradients the wind‐driven currents are larger and the response resembles a baroclinic flow pattern. Currents driven by river flows are sheared and also have a nonlinear response pattern. Only near‐surface currents are driven seaward by discharges below 3000 m3/s. At higher discharge rates, surface current variability uncouples from the river flow and the increased discharge rates drive near‐bed current seaward. This change in the river‐forced flow pattern may be associated with a hydraulic jump in the

ISSN:0148-0227    

DOI:10.1029/96JC02506

年代:1996

数据来源: WILEY

摘要:

We study the convective overturning of a rotating stratified fluid in the laboratory. Convection is induced from the surface of a salt‐stratified fluid by the introduction of salty fluid over a circular area. The external parameters are buoyancy forcing of strength,B0, applied over a circular area of radiusRs, the rotation rate as measured byf, ambient stratificationN, and the depthH. The experiments are motivated by physical scaling arguments which attempt to predict the length and velocity scales of the convective chimney as it adjusts under gravity and rotation and breaks up through baroclinic instability. The scales of interest include the number, size, and typical speeds of the fragments of the broken chimney, the final depth of penetration of the convective mixed layer, and the total volume of convectively produced water. These scales are tested against the laboratory experiments and found to be appropriate. In this idealized problem we have found the depth of penetration depends only on the size and strength of the forcing and the ambient stratification encountered by the convection event; it does not depend explicitly on rotation. The implications of the work to deep water formation in the Labrador Sea and elsewhere are discussed. Finally, the study has relevance to the role and representation of baroclinic eddies in large‐scale circulation of the oc

ISSN:0148-0227    

DOI:10.1029/96JC02322

年代:1996

数据来源: WILEY