摘要:

Solutions for edge waves trapped on a concave upward exponential topography (type a) were given by Ball in 1967. This study extends Ball's solutions to convex upward exponential topographies (type b). Similar results are found in terms of eigenmodes, cutoff frequencies, etc., in both cases, but a new phenomenon which was not found in the previous solutions, stopping zones of frequency, is found for the present case. In addition, the group velocity shows far more structure for convex upward exponential topography.

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00916

年代:1986

数据来源: WILEY

摘要:

Measurements of the ocean wave‐radar modulation transfer functionMat 4.3 GHz (C band) carried out in the North Sea are presented here. It was found that the values forMfor C band lie within the same range as for X, L, and Kabands. The measurements were made at incidence angles of 54° (HH and VV polarization) and 40° (VV polarization only). It was found thatMdecreases with increasing wind speedUand ocean wave frequency ƒ. The phase ofMwas such that maximum backscatter occurs at the forward (leeward) face of the long ocean waves. For small dimensionless frequencies, ƒ* = (ƒU)/g, the modulus ofMreaches values of up to 30. This indicates that there is a source of strong hydrodynamic modulation, most probably wind induced, that is as yet unexplained by existing th

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00923

年代:1986

数据来源: WILEY

摘要:

Application of the parabolic equation method to wave propagation problems implies that the propagation direction of all major components of the wave field must be confined to some narrow band of directions centered on a prechosen principal propagation direction. The allowed directional bandwidth is then delimited by the maximum allowed error in the principal direction wavelength when a transverse wavelength (wave turned at an angle) is imposed. In this paper we investigate higher‐order approximations which have the effect of opening the directional bandwidth to better than 45° around the principal direction and which fit within the computational framework of the lower‐order approximation. The problem is discussed within the context of the pure‐diffraction limit (constant depth), after which a higher‐order scheme is provided for waves in domains with slowly varying depth and ambient current. Several computational examples are provided to show the improvements in the higher‐order approximation relative to the existing lower‐order approximation. We then examine several forms of computational noise which arise in practical applications of either higher‐ or lower‐order approximations and suggest methods for suppressing the nonphysical, computational modes

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00933

年代:1986

数据来源: WILEY

摘要:

Internal gravity wave motions in a two‐dimensional vertical plane of fluid having constant mean Brunt‐Vaisala frequency are numerically simulated. The waves are integrated to statistical equilibrium under forcing and dissipation with forcing applied to low wave number modes. The model is used to study the variation of the internal wave energy dissipation rate with the Richardson numberRi, the effect of nonlinear wave interaction on the wave frequency, the wave number spectrum of the buoyancy flux, and the balance of the spectral energy flux. The energy dissipation rate is shown by our simulations to vary strongly nearRi≈ 1 and to increase proportionally toRi−1. The rms frequency fluctuation is found to increase approximately linearly withRi−1/2and with the wave number magnitude. The simulations show that the buoyancy flux varies nonuniformly with wave numbers, kinetic to potential energy conversion occurs mostly at low wave numbers, and an opposite conversion occurs in the rest of the wave number space. The mean spectral energy balance in the region where negative conversion occurs is marked by positive (gain) potential energy transfer and negative (loss) kinetic energy transfer in the intermediate wave number range and positive transfer for both kinetic and potential energy in the high wave number range; the latter is balanced by dissipation. The spectra of kinetic and potential energy are presented. The similarity in the slope of the kinetic energy spectra between the stratified turbulence from our simulation and the two‐dimensional unstratified, homogeneous turbulen

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00953

年代:1986

数据来源: WILEY

摘要:

Scatter plots of satellite multispectral microwave emissivities at two or three different frequencies and/or polarizations reveal unique clusters that are persistent throughout winter conditions in the Arctic region. Cluster analysis of both global and regional data shows that there are more than one radiometrically different types of multiyear ice in the central Arctic, reflecting the strong effect of volume scattering, which varies with the size and shape of the inhomogeneities in the material as well as with the overall structure and history of formation. Some of the clusters in the central Arctic also exhibit “hook patterns” in 18‐GHz versus 37‐GHz plots, indicating sensitivity to modification of the signature by some surface and subsurface effects at 37 GHz. Sensitivity to snow cover and other surface effects in the first‐year ice region is also evident at 37 GHz. A coplanarity test using three SMMR channels shows the potential as well as limitation of the sensor in discriminating different ice types. However, the capability for accurate determination of sea ice concentration, especially in the central Arctic, is evident from scatter plots of the emissivities using the two polarizations at 37 GHz. The consolidated ice data in the central Arctic form a very compact and linear set of points in these plots, and they slope the same way throughout the winter of 1979 and in other years (1980–1984). An ice concentration algorithm based on the utilization of this slope (∼1.03) is developed that yields retrieved values with an accuracy of about 5% in the central Arctic and 10% in the seasonal sea ice region. The total areal ice extent and actual ice cover were also derived from ice concentrations retrieved by using the algorithm, and the results from several years of midwinter data show a relatively stable ice cover in the northe

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00975

年代:1986

数据来源: WILEY

摘要:

The work of Longuet‐Higgins (1963) on the effects of wave nonlinearity on the statistics of the sea surface is extended here to obtain the joint distribution of surface elevation and slopes for a nonlinear random sea. The results are used to examine the effect of wave nonlinearity on the form of a radar altimeter pulse which is reflected from the sea surface. It is shown how wave information may be derived from the return pulse and how this can be used to correct errors in the altimeter mean sea level estimate (a problem known as “sea state bia

ISSN:0148-0227    

DOI:10.1029/JC091iC01p00995

年代:1986

数据来源: WILEY

摘要:

Optical studies of the suspended load in the Gulf of Maine have been performed in conjunction with hydrographic and biological analyses between late winter and early fall. Major particle sources are coastal runoff, benthic resuspension, and biological activity. Analysis of the optical efficiencies of the particles suggests that runoff and resuspension sources are restricted to the nearshore and shallow regions. The variabilities in the coupling and discoupling of the optical and hydrographic features of the Gulf demonstrate that advection is primarily responsible for the distribution of clear water masses, while settling, vertical mixing, and productivity are the processes behind the distribution of particles.

ISSN:0148-0227    

DOI:10.1029/JC091iC01p01007

年代:1986

数据来源: WILEY

摘要:

The action of wind stress upon the marine surface is responsible for producing air bubbles in seawater through wave breaking. After a given residence time in the sea, bubbles return to the surface, where they burst. The phenomenon of bursting produces two families of droplets: film drops and jet drops. The characteristics of jet drops are far better known than those of film drops. By means of an in‐line holographic technique one can obtain experimental results through visualization. One can observe the successive stages of the bursting process of a single bubble in deionized fresh water and in seawater. One visualizes both film drops and jet drops generated by bubbles whose diameter may attain 10 mm. The onset of the bursting phenomenon is clearly shown. Film drop count and size are measurable and may be compared with other available estimate

ISSN:0148-0227    

DOI:10.1029/JC091iC01p01019

年代:1986

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JC091iC01p01030

年代:1986

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JC091iC01p01033

年代:1986

数据来源: WILEY