On thermally forced stratified rotating fluids
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0LR(1980)27(12) A. Physical Oceanography 855 A phase-coded signal with 64-ms resolution was transmitted at 10-rain intervals for a 48-day period between an acoustic source moored at 2000-m depth and a bottom-mounted receiver at ~ 3000-m depth and at -~900-kin range. About 16 multipaths were resolved; they were stable in the presence of ocean fluctuations and could be identified (with some exceptions) from ray theory. Precision to which daily travel-time fluctuations along mul- tipaths could be measured was better than 10 ms. Resolution, stability, identification, and precision are adequate for acoustic monitoring of mesoscale ocean variability by measuring travel-time variations along ray paths. Department of Ocean Engineering, Woods Hole Oceanographic Institu- tion, Woods Hole, Mass. 02543, U.S.A. 80:5830 Stickler, D. C. and E. Ammicht, 1980. Uniform asymptotic evaluation of the continuous spectrum contribution for the Pekeris model. J. acoust. Soc. Am., 67(6): 2018-2024. Determining the continuous spectral contribution to transmission loss in ocean acoustics can be very difficult. The proposed uniform asymptotic method exploits the fact that there are singularities near the integrand of an integral representation of continuous spectrum and that these singularities determine the asymptotic behavior of the continuous spectrum. Numerical examples illustrate proper, real improper, and complex improper mode influences on the con- tinuous spectrum. The technique avoids the sometimes costly numerical evaluation of the con- tinuous spectral contribution. Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, N.Y. 10012, U.S.A. 80:5831 Young, H. J., 1980. Measurements of underwater signal phase stability using a moving source. J. acoust. Soc. Am., 67(6): 2025-2028. Using a cw source suspended from a drifting ship, phase angles of the signals at four hydrophones on the bottom in a horizontal line were compared. The technique canceled out the Doppler shift by using the combined outputs of all hydrophones as a phase reference signal and enabled a comparison of the phase angles of signals arriving over multiple paths. An empirical expression was selected to fit the experimental results and permit interpolation to obtain values for other hydrophone spacings. 44 Central Ave., Morris Plains, N.J. 07950, U.S.A. 80:5832 Zhou, Jixun, 1979. Vertical coherence of long- range reverberation in the shallow-water homogeneous layer. (In Chinese; English abstract.) Acta oceanol, sin., 1(2): 212-218. Applicable to analyses of the 'angular dependence of bottom (or surface) scattering at low grazing angle,' the angular power spectrum for the shallow- water averaged acoustic field is used to determine long-range reverberation vertical coherence. Institute of Acoustics, Academia Sinica, People's Republic of China. (izs) 18. Fluid mechanics 80:5833 Kraichman, R. H. and David Montgomery, 1980. Two-dimensional turbulence. (Review.) Repts Prog. Phys., 43(5): 547-619. Unrealized in nature or in the laboratory, two- dimensional turbulence exists only in computer simulations but is important for its idealization of geophysical phenomena. Including discussions of basic dynamic equations, turbulent diffusion and cascades, predictability theory, turbulence on a rotating sphere, two-dimensional superflow, ab- solute statistical equilibrium and spectral transport of energy and enstrophy, the review con- cludes with some hydrodynamic applications and the admonition that 'idealized theory may be more valid in providing a language for discussion rather than a true explanation.' Includes ca. 250 refer- ences. Dublin, N.H. 034~, U.S.A. (izs) 80:5834 Rahm, Lars and Gosta Walin, 1980. On thermally forced stratified rotating fluids. J. Fluid Mech., 97(4): 807°828. Axisymmetric steady motion of an inhomogeneous rotating fluid is considered. A system of equations, with appropriate boundary conditions, controlling the smooth interior fields is derived under the assumption of small dissipation and small side- boundary conductance. It is argued that this system, being derived without linearization of the equations, might form the basis of valuable numerical analysis. Assuming sufficiently weak forcing, i.e., high insulation of the non-horizontal boundaries, a linear system is derived. Department of Oceanography, University of Gothenburg, Sweden.
Transcript of On thermally forced stratified rotating fluids
0LR(1980)27(12) A. Physical Oceanography 855
A phase-coded signal with 64-ms resolution was transmitted at 10-rain intervals for a 48-day period between an acoustic source moored at 2000-m depth and a bottom-mounted receiver at ~ 3000-m depth and at -~ 900-kin range. About 16 multipaths were resolved; they were stable in the presence of ocean fluctuations and could be identified (with some exceptions) from ray theory. Precision to which daily travel-time fluctuations along mul- tipaths could be measured was better than 10 ms. Resolution, stability, identification, and precision are adequate for acoustic monitoring of mesoscale ocean variability by measuring travel-time variations along ray paths. Department of Ocean Engineering, Woods Hole Oceanographic Institu- tion, Woods Hole, Mass. 02543, U.S.A.
80:5830 Stickler, D. C. and E. Ammicht, 1980. Uniform
asymptotic evaluation of the continuous spect rum contr ibut ion for the Pekeris model. J. acoust. Soc. Am., 67(6): 2018-2024.
Determining the continuous spectral contribution to transmission loss in ocean acoustics can be very difficult. The proposed uniform asymptotic method exploits the fact tha t there are singularities near the integrand of an integral representation of continuous spectrum and that these singularities determine the asymptotic behavior of the continuous spectrum. Numerical examples illustrate proper, real improper, and complex improper mode influences on the con- tinuous spectrum. The technique avoids the sometimes costly numerical evaluation of the con- tinuous spectral contribution. Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, N.Y. 10012, U.S.A.
80:5831 Young, H. J., 1980. Measurements of underwater
signal phase stability using a moving source. J. acoust. Soc. Am., 67(6): 2025-2028.
Using a cw source suspended from a drifting ship, phase angles of the signals at four hydrophones on the bottom in a horizontal line were compared. The technique canceled out the Doppler shift by using the combined outputs of all hydrophones as a phase reference signal and enabled a comparison of the phase angles of signals arriving over multiple paths. An empirical expression was selected to fit the experimental results and permit interpolation to obtain values for other hydrophone spacings. 44 Central Ave., Morris Plains, N.J. 07950, U.S.A.
80:5832 Zhou, Jixun, 1979. Vertical coherence of long-
range reverberation in the shallow-water homogeneous layer. (In Chinese; English abstract.) Acta oceanol, sin., 1(2): 212-218.
Applicable to analyses of the 'angular dependence of bottom (or surface) scattering at low grazing angle,' the angular power spectrum for the shallow- water averaged acoustic field is used to determine long-range reverberation vertical coherence. Institute of Acoustics, Academia Sinica, People's Republic of China. (izs)
18. Fluid mechanics
80:5833 Kraichman, R. H. and David Montgomery, 1980.
Two-dimensional turbulence. (Review.) Repts Prog. Phys., 43(5): 547-619.
Unrealized in nature or in the laboratory, two- dimensional turbulence exists only in computer simulations but is important for its idealization of geophysical phenomena. Including discussions of basic dynamic equations, turbulent diffusion and cascades, predictability theory, turbulence on a rotating sphere, two-dimensional superflow, ab- solute statistical equilibrium and spectral transport of energy and enstrophy, the review con- cludes with some hydrodynamic applications and the admonition that 'idealized theory may be more valid in providing a language for discussion rather than a true explanation.' Includes ca. 250 refer- ences. Dublin, N.H. 034~, U.S.A. (izs)
80:5834 Rahm, Lars and Gosta Walin, 1980. On thermally
forced stratified rotating fluids. J. Fluid Mech., 97(4): 807°828.
Axisymmetric steady motion of an inhomogeneous rotating fluid is considered. A system of equations, with appropriate boundary conditions, controlling the smooth interior fields is derived under the assumption of small dissipation and small side- boundary conductance. It is argued that this system, being derived without linearization of the equations, might form the basis of valuable numerical analysis. Assuming sufficiently weak forcing, i.e., high insulation of the non-horizontal boundaries, a linear system is derived. Department of Oceanography, University o f Gothenburg, Sweden.
