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Critical levels of internal Alfvén-gravity waves in shear flow
OLR (1987) 34 (9)
A. Physical Oceanography
The long-wave equations including curvature effects are introduced to describe the deformation and fission of a barotropic solitary wave passing over a shelf or obstacle. Numerical results are in good agreement with an analytical model derived by Germain (1984) in the framework of a generalized shallow-water theory, and with experimental results collected in a large channel equipped with a wave generator. Given the initial conditions, it is possible to predict the amplitude and number of the transmitted solitary waves as well as the amplitude of the reflected wave, and to describe the shape of the free surface at any time. Inst. de Mecanique de Grenoble, B.P. 68, 38402 Saint-Martin d'Heres Cedex, France. 87:4915 Shillington, F.A. and G.B. Brundrit, 1986. Energy flux of edge waves travelling along a continental shelf. Geophys. astrophys. Fluid Dynam, 37(3): 2 i 9-236. Longuet-Higgins (1964) originally recognised that the energy flux defined by pressure work from the equations of motion was not the same as the mean energy density times the group velocity for planetary waves on a beta-plane. This paper addresses a similar paradox for linear, long period edge waves on an arbitrarily shaped (in the offshore direction) straight continental shelf. The approach is to first examine a wavetrain solution to the problem and then to use a multiple scale argument which results in a solution as a group of waves modulated about a central frequency and wavenumber. The paradox is resolved in both instances by noting that a divergence-free quantity can be included in the energy conservation equation to establish an equivalence between the two definitions of mean energy flux. We discuss which energy flux definition is preferable in a given situation. Oceanogr. Dept., Univ. of Cape Town, Rondebosch 7700, South Africa. 87:4916 Wang, Xinian and Fengshu Liu, 1986. Preliminary study on typhoon surges along the Fujian and Guandong coastal areas. Stud. mar. sin, 27:33-44. (In Chinese, English abstract.) Mar. Environ. Forecasting Centre, Natl. Bur. of Oceanogr., People's Republic of China. 87:4917 Xu, Delun, P.A. Hwang and Jin Wu, 1986. Breaking of wind-generated waves. J. phys. Oceanogr., 16(12):2172-2178. The critical surface slope and global wave steepness for inception of breaking were evaluated in a laboratory tank. Besides the frequency of occurrence, two other characteristic quantities, height and
737
duration of breaking, were measured. The frequency of breaking was found to increase rapidly with wind velocity; the period of breaking remained about 7% of the wave period at all wind velocities. The height of breaking was about 30% of the wave height. Shandong College of Oceanogr., Qingdao, Shandong, People's Republic of China.
AI80. Internal waves and tides 87:4918 Brink, K.H., 1986. Topographic drag due to barntropic flow over the continental shelf and slope. J. phys. Oceanogr., 16(12):2150-2158. A barotropic model is formulated to investigate the drag due to steady barotropic alongshore flow over extensive, irregular, small-amplitude topography. Topographic drag is in general appreciable only when the mean flow runs counter to the direction of free shelf-wave phase propagation. The cross-shelf structure of the drag is determined by which mode lee waves dominate. This selection is determined by the projection of the topographic structure onto the wave mode, and by the degree of matching between dominant topographic length scale and natural lee wave wavelength. WHOI, Woods Hole, MA 02543, USA. 87:4919 Venkatachalappa, M., 1987. Critical levels of internal Affv6n-gravity waves in shear flow. Geophys. astrophys. Fluid Dynam., 38(1):25-41. UGC-DSA Centre in Fluid Mechanics, Dept. of Math., Bangalore Univ., Bangalore 560001, India.
A240. Optical properties 87:4920 Siegel, Herbert and H.-J. Brosin, 1986. Regional differences in the spectral reflectance of seawater. Beitr. Meeresk., 55:71-77. Reflectances from different sea areas (eastern central Atlantic Ocean, upwelling area off Mauritania and the Baltic Sea) are compared. Differences between the spectral curves result from the nature and properties of the water bodies. The water masses are differentiated according to nature and origin of dissolved and suspended matter (phytoplankton, sediment, yellow substances) based on a classification proposed by Morel and Prieur (1977). Akad. der Wissensehaften, Inst. fur Meereskunde, DDR2530 Rostock-Warnemunde, DRG.
A. Physical Oceanography
The long-wave equations including curvature effects are introduced to describe the deformation and fission of a barotropic solitary wave passing over a shelf or obstacle. Numerical results are in good agreement with an analytical model derived by Germain (1984) in the framework of a generalized shallow-water theory, and with experimental results collected in a large channel equipped with a wave generator. Given the initial conditions, it is possible to predict the amplitude and number of the transmitted solitary waves as well as the amplitude of the reflected wave, and to describe the shape of the free surface at any time. Inst. de Mecanique de Grenoble, B.P. 68, 38402 Saint-Martin d'Heres Cedex, France. 87:4915 Shillington, F.A. and G.B. Brundrit, 1986. Energy flux of edge waves travelling along a continental shelf. Geophys. astrophys. Fluid Dynam, 37(3): 2 i 9-236. Longuet-Higgins (1964) originally recognised that the energy flux defined by pressure work from the equations of motion was not the same as the mean energy density times the group velocity for planetary waves on a beta-plane. This paper addresses a similar paradox for linear, long period edge waves on an arbitrarily shaped (in the offshore direction) straight continental shelf. The approach is to first examine a wavetrain solution to the problem and then to use a multiple scale argument which results in a solution as a group of waves modulated about a central frequency and wavenumber. The paradox is resolved in both instances by noting that a divergence-free quantity can be included in the energy conservation equation to establish an equivalence between the two definitions of mean energy flux. We discuss which energy flux definition is preferable in a given situation. Oceanogr. Dept., Univ. of Cape Town, Rondebosch 7700, South Africa. 87:4916 Wang, Xinian and Fengshu Liu, 1986. Preliminary study on typhoon surges along the Fujian and Guandong coastal areas. Stud. mar. sin, 27:33-44. (In Chinese, English abstract.) Mar. Environ. Forecasting Centre, Natl. Bur. of Oceanogr., People's Republic of China. 87:4917 Xu, Delun, P.A. Hwang and Jin Wu, 1986. Breaking of wind-generated waves. J. phys. Oceanogr., 16(12):2172-2178. The critical surface slope and global wave steepness for inception of breaking were evaluated in a laboratory tank. Besides the frequency of occurrence, two other characteristic quantities, height and
737
duration of breaking, were measured. The frequency of breaking was found to increase rapidly with wind velocity; the period of breaking remained about 7% of the wave period at all wind velocities. The height of breaking was about 30% of the wave height. Shandong College of Oceanogr., Qingdao, Shandong, People's Republic of China.
AI80. Internal waves and tides 87:4918 Brink, K.H., 1986. Topographic drag due to barntropic flow over the continental shelf and slope. J. phys. Oceanogr., 16(12):2150-2158. A barotropic model is formulated to investigate the drag due to steady barotropic alongshore flow over extensive, irregular, small-amplitude topography. Topographic drag is in general appreciable only when the mean flow runs counter to the direction of free shelf-wave phase propagation. The cross-shelf structure of the drag is determined by which mode lee waves dominate. This selection is determined by the projection of the topographic structure onto the wave mode, and by the degree of matching between dominant topographic length scale and natural lee wave wavelength. WHOI, Woods Hole, MA 02543, USA. 87:4919 Venkatachalappa, M., 1987. Critical levels of internal Affv6n-gravity waves in shear flow. Geophys. astrophys. Fluid Dynam., 38(1):25-41. UGC-DSA Centre in Fluid Mechanics, Dept. of Math., Bangalore Univ., Bangalore 560001, India.
A240. Optical properties 87:4920 Siegel, Herbert and H.-J. Brosin, 1986. Regional differences in the spectral reflectance of seawater. Beitr. Meeresk., 55:71-77. Reflectances from different sea areas (eastern central Atlantic Ocean, upwelling area off Mauritania and the Baltic Sea) are compared. Differences between the spectral curves result from the nature and properties of the water bodies. The water masses are differentiated according to nature and origin of dissolved and suspended matter (phytoplankton, sediment, yellow substances) based on a classification proposed by Morel and Prieur (1977). Akad. der Wissensehaften, Inst. fur Meereskunde, DDR2530 Rostock-Warnemunde, DRG.