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A note on the reflection of low-frequency equatorial Rossby waves from realistic western boundaries
520
A. PhysicalOceanography
to include interactions up to an arbitrary order in wave steepness. A large number of free wave modes are typically used whose amplitude evolutions are determined through a pseudospectral treatment of the nonlinear free-surface conditions. Method efficiency and accuracy are demonstrated by comparisons to fully nonlinear semi-Lagrangian computations; calculations of long-time evolution of wavetrains using the modified Zakharov equations; and experimental measurements of a travelling wave packet. Nonlinear interactions between two colliding wave envelopes of different carrier frequencies are also considered. Dept. of Ocean Engng, MIT, Cambridge, M A 02139, USA. 88:3257 Fenton, J.D. and R.J. Sobey (comments), 1988. Discussion of 'Nonuniqneness in stream function wave theoD',' by R.A. Dalrymple and Pedro Solara. J. WatWay Port coast. Ocean Engng, Am. Soc. civ. Engrs, 114(1):110-114. 88:3258 Gent, P.R., 1987. Forcing and friction effects on vertically propagating waves in the equatorial oceans. J. phys. Oceanogr., 17(11):1897-1908. A new projection onto the meridional eigenfunctions of the pressure equation, derived for a single Fourier wave component, demonstrates that the solution is regular and not singular at the inertial latitudes, and is more convenient to use than the corresponding projection onto the meridional velocity equation. The wavenumber spectrum from the resulting forced vertical structure equation, found for four choices of vertical profile for the body force, is insensitive to the particular profile chosen. The projection is used to study the effects of forcing and linear damping on the vertical propagation of space-time transformed energy in three wave modes: Kelvin, first Rossby and mixed Rossby-gravity waves. With constant buoyancy frequency, energy decay is exponential in depth with the coefficient proportional to the damping magnitude. Linear damping effects are very different on each wave. Thus, it is fallacious to make deductions about meridional phase changes in the total solution to a general forced problem from the phase changes of each wave component. NCAR, Boulder, CO 80307, USA. 88:3259 Hudspeth, R.T., J.H, Nath and P. Khare, 1988. Wave phase/amplitude effects on force coefficients. J. Wat Way Port coast. Ocean Engng, A m. Soc. cir. Engrs, 114(1):34-49. An algorithm to compute force coefficients for the two-term Morison equation for a cylinder in waves
OLR (1988)35 (6)
illustrates the parametric dependence of force coefficient estimates on the Dean eccentricity parameter and their sensitivity to phase/amplitude measurements of the ambient wave. The algorithm is based on linear regression analysis of error in the computed force assuming that the Morison equation and linear wave theory represent the 'true' force and wave kinematics exactly. Ocean Engng Prog., Dept. of Civ. Engng, Oregon State Univ., Corvallis, OR 97331, USA. (emm) 88:3260 Janssen, P.A.E.M., 1987. The initial evolution of gravity--capillary waves. J. Fluid Mech., 184: 581 597. Discussed here is the initial evolution of windgenerated, gravity-capillary waves by means of a dynamical model that includes the effects of wind input, viscous dissipation and three-wave interactions. Studies of the generation of the initial wavelets by wind reveal that under certain conditions a sudden migration of the peak wavenumber is found, related to the phenomenon of second-harmonic resonance. During the generation of the initial wavelets by wind, nonlinear three-wave interactions may be important. Therefore, the experimental determination of the growth rate of the waves by wind by just analysing the time series of the surface elevation might be in error. ECMWF, Shinfield Park, Reading, UK. 88:3261 Kirby, J.T. (comment), 1988. Discussion of 'Refraction--diffraction model for linear water waves,' by B,A. Ebersole. J. WatWay Port coast. Ocean Engng, Am. Soc. civ. Engrs, l l4(1):101-103. 88:3262 McCalpin, J.D., 1987. A note on the reflection of low-frequency equatorial Rosshy waves from realistic western boundaries. J. phys. Oceanogr., 17(11): 1944-1949. The analytic theory of Cane and Gent on the reflection of low frequency equatorial waves from arbitrary boundaries is applied to the reflection of long Rossby waves from realistic approximations to the western boundaries of the Atlantic, Pacific, and Indian oceans. Results show that low-frequency, first meridional mode, first baroclinic mode reflection is close to that of a straight north-south boundary in all three basins. Increasing the frequency, meridional mode number, a n d / o r vertical mode number causes drastic changes in the energy flux reflection coefficients. Corresponding to the general slope and complexity of the coastline, effects are greatest for the Pacific Ocean and least for the Indian Ocean.
OLR (1988)35 (6)
A. PhysicalOceanography
Mesoscale Air-Sea Interaction Group, Florida State Univ., Tallahassee, FL 32306, USA. 88:3263 Michida, Yutaka, Masayuki Tokuda, Yoshizo Ueno and Haruo Ishii, 1987. A Tucker type ship-borne wave recorder. II. Comparative experiment with the visual observation and a buoy wave meter. Rept natn. Res. Cent. Disaster Prevent., Tokyo, 39:171-182. (In Japanese, English abstract.) Hydrographic Dept., Maritime Safety Agcy. of Japan, Chuo-ku, Tokyo 104, Japan. 88:3264 Nielsen, Peter (comment), 1988. Discussion of 'Wave number of linear progressive waves,' by ChungShang Wu and E,B. Thornton. J. Wat Way Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1): 115-116. 88:3265 Reason, C.J.C., L.A. Mysak and P.F. Cummins, 1987. Generation of annual-period Rossby waves in the South Atlantic Ocean by the wind stress curl. J. phys. Oceanogr., 17(11):2030-2042. The forcing wind field for 15°-51°S, 45°W-41°E was used to drive a linear, reduced-gravity model of the South Atlantic and southwest Indian oceans. In the South Atlantic, the response consists of long Rossby waves, which generally propagate southwestward and exhibit refraction of wave energy toward the Equator. Short Rossby waves with eastward energy propagation are generated in the small area of the Indian Ocean included in the model. Medium to short waves generated southeast of Africa reflect their energy into the Indian Ocean. The most efficient wave generators are the wind stress curl maxima (1) off the Namibian coast near 25°S, 10°E; (2) near the Agulhas Plateau at 38°S, 25°E; and (3) in the South Atlantic Ocean interior near 38°S, 10°W. Dept. of Geogr., Univ. of British Columbia, Vancouver, BC V6T IW5, Canada. 88:3266 Resio, D.T., 1988. Shallow-water waves. II: Data comparisons. J. WatWay Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1):50-65. Predicted spectral shapes appear to agree well with those measured under storm conditions. Results indicate that, under such conditions, a dynamic balance between wind input and nonlinear fluxes dominates the shape of a spectrum and controls the total energy level and related energy losses in waves propagating into shallow water, even into depths less than 33 ft. Nonlinear flux estimates provide a quantitative means of evaluating energy losses, even
521
in nonequilibrium conditions, particularly important in modeling waves in complex bathymetries, in situations of mixed sea-swell, or when wave generation is taking place at very oblique angles to the coast, and in very shallow water where nonlinear fluxes can no longer maintain an equilibrium. Offshore and Coastal Tech., Inc., 911 Clay St., Vicksburg, MS 39180, USA. 88:3267 Sebekin, B.I., 1986. Influence of wave dispersion on directional tsunami propagation. Izv. Atmos. Ocean Phys. (a translation of Fiz. Atrnos. Okeana), 22(9):743-748. Inst. of Oceanol., Acad. of Sci., USSR. 88:3268 Slabakov, H.D., 1986. Assessment of the parameters of the autocorrelation and spectral functions of sea motion. Oceanology, Sofia, 16:74-83. (In Bulgarian, English abstract.) 88:3269 Smith, O.P., 1988. Duration of extreme wave conditions. J. WatWay Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1):1-17. Statistical trends of the duration of extreme wave conditions, as characterized by hindcast wave information, are investigated at five sites along the U.S. coast. Identification of events and definition of their durations are based on a threshold for zero moment wave heights; the percentage exceedance above a specified threshold is roughly 30% of the average number of events per year, regardless of geographical location. The extremal type I distribution function is applied to model both the distribution of durations and of peak zero moment wave heights. The assumption of independence of duration from peak event intensity is proposed for estimating durations of zero moment wave heights above a threshold, given a peak zero moment wave height. 2130 Pony Farm Rd., Clayton, NC 27520, USA. 88:3270 Wtlbber, Chresten, 1986. [A numerical model for the investigation of baroclinic Rossby waves in the North Atlantic.] Bet. Inst. Meeresk. ChristianAlbrechts-Univ., 159:96pp. (In German, English abstract.) A linear, quasigeostrophic model describing windinduced, baroclinic Rossby waves in a closed basin is applied to the North Atlantic between 5 ° and 45°N, using the annual cycle of the wind stress curl as forcing function. Due to the large spatial scales of the wind field, Rossby waves are only generated
A. PhysicalOceanography
to include interactions up to an arbitrary order in wave steepness. A large number of free wave modes are typically used whose amplitude evolutions are determined through a pseudospectral treatment of the nonlinear free-surface conditions. Method efficiency and accuracy are demonstrated by comparisons to fully nonlinear semi-Lagrangian computations; calculations of long-time evolution of wavetrains using the modified Zakharov equations; and experimental measurements of a travelling wave packet. Nonlinear interactions between two colliding wave envelopes of different carrier frequencies are also considered. Dept. of Ocean Engng, MIT, Cambridge, M A 02139, USA. 88:3257 Fenton, J.D. and R.J. Sobey (comments), 1988. Discussion of 'Nonuniqneness in stream function wave theoD',' by R.A. Dalrymple and Pedro Solara. J. WatWay Port coast. Ocean Engng, Am. Soc. civ. Engrs, 114(1):110-114. 88:3258 Gent, P.R., 1987. Forcing and friction effects on vertically propagating waves in the equatorial oceans. J. phys. Oceanogr., 17(11):1897-1908. A new projection onto the meridional eigenfunctions of the pressure equation, derived for a single Fourier wave component, demonstrates that the solution is regular and not singular at the inertial latitudes, and is more convenient to use than the corresponding projection onto the meridional velocity equation. The wavenumber spectrum from the resulting forced vertical structure equation, found for four choices of vertical profile for the body force, is insensitive to the particular profile chosen. The projection is used to study the effects of forcing and linear damping on the vertical propagation of space-time transformed energy in three wave modes: Kelvin, first Rossby and mixed Rossby-gravity waves. With constant buoyancy frequency, energy decay is exponential in depth with the coefficient proportional to the damping magnitude. Linear damping effects are very different on each wave. Thus, it is fallacious to make deductions about meridional phase changes in the total solution to a general forced problem from the phase changes of each wave component. NCAR, Boulder, CO 80307, USA. 88:3259 Hudspeth, R.T., J.H, Nath and P. Khare, 1988. Wave phase/amplitude effects on force coefficients. J. Wat Way Port coast. Ocean Engng, A m. Soc. cir. Engrs, 114(1):34-49. An algorithm to compute force coefficients for the two-term Morison equation for a cylinder in waves
OLR (1988)35 (6)
illustrates the parametric dependence of force coefficient estimates on the Dean eccentricity parameter and their sensitivity to phase/amplitude measurements of the ambient wave. The algorithm is based on linear regression analysis of error in the computed force assuming that the Morison equation and linear wave theory represent the 'true' force and wave kinematics exactly. Ocean Engng Prog., Dept. of Civ. Engng, Oregon State Univ., Corvallis, OR 97331, USA. (emm) 88:3260 Janssen, P.A.E.M., 1987. The initial evolution of gravity--capillary waves. J. Fluid Mech., 184: 581 597. Discussed here is the initial evolution of windgenerated, gravity-capillary waves by means of a dynamical model that includes the effects of wind input, viscous dissipation and three-wave interactions. Studies of the generation of the initial wavelets by wind reveal that under certain conditions a sudden migration of the peak wavenumber is found, related to the phenomenon of second-harmonic resonance. During the generation of the initial wavelets by wind, nonlinear three-wave interactions may be important. Therefore, the experimental determination of the growth rate of the waves by wind by just analysing the time series of the surface elevation might be in error. ECMWF, Shinfield Park, Reading, UK. 88:3261 Kirby, J.T. (comment), 1988. Discussion of 'Refraction--diffraction model for linear water waves,' by B,A. Ebersole. J. WatWay Port coast. Ocean Engng, Am. Soc. civ. Engrs, l l4(1):101-103. 88:3262 McCalpin, J.D., 1987. A note on the reflection of low-frequency equatorial Rosshy waves from realistic western boundaries. J. phys. Oceanogr., 17(11): 1944-1949. The analytic theory of Cane and Gent on the reflection of low frequency equatorial waves from arbitrary boundaries is applied to the reflection of long Rossby waves from realistic approximations to the western boundaries of the Atlantic, Pacific, and Indian oceans. Results show that low-frequency, first meridional mode, first baroclinic mode reflection is close to that of a straight north-south boundary in all three basins. Increasing the frequency, meridional mode number, a n d / o r vertical mode number causes drastic changes in the energy flux reflection coefficients. Corresponding to the general slope and complexity of the coastline, effects are greatest for the Pacific Ocean and least for the Indian Ocean.
OLR (1988)35 (6)
A. PhysicalOceanography
Mesoscale Air-Sea Interaction Group, Florida State Univ., Tallahassee, FL 32306, USA. 88:3263 Michida, Yutaka, Masayuki Tokuda, Yoshizo Ueno and Haruo Ishii, 1987. A Tucker type ship-borne wave recorder. II. Comparative experiment with the visual observation and a buoy wave meter. Rept natn. Res. Cent. Disaster Prevent., Tokyo, 39:171-182. (In Japanese, English abstract.) Hydrographic Dept., Maritime Safety Agcy. of Japan, Chuo-ku, Tokyo 104, Japan. 88:3264 Nielsen, Peter (comment), 1988. Discussion of 'Wave number of linear progressive waves,' by ChungShang Wu and E,B. Thornton. J. Wat Way Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1): 115-116. 88:3265 Reason, C.J.C., L.A. Mysak and P.F. Cummins, 1987. Generation of annual-period Rossby waves in the South Atlantic Ocean by the wind stress curl. J. phys. Oceanogr., 17(11):2030-2042. The forcing wind field for 15°-51°S, 45°W-41°E was used to drive a linear, reduced-gravity model of the South Atlantic and southwest Indian oceans. In the South Atlantic, the response consists of long Rossby waves, which generally propagate southwestward and exhibit refraction of wave energy toward the Equator. Short Rossby waves with eastward energy propagation are generated in the small area of the Indian Ocean included in the model. Medium to short waves generated southeast of Africa reflect their energy into the Indian Ocean. The most efficient wave generators are the wind stress curl maxima (1) off the Namibian coast near 25°S, 10°E; (2) near the Agulhas Plateau at 38°S, 25°E; and (3) in the South Atlantic Ocean interior near 38°S, 10°W. Dept. of Geogr., Univ. of British Columbia, Vancouver, BC V6T IW5, Canada. 88:3266 Resio, D.T., 1988. Shallow-water waves. II: Data comparisons. J. WatWay Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1):50-65. Predicted spectral shapes appear to agree well with those measured under storm conditions. Results indicate that, under such conditions, a dynamic balance between wind input and nonlinear fluxes dominates the shape of a spectrum and controls the total energy level and related energy losses in waves propagating into shallow water, even into depths less than 33 ft. Nonlinear flux estimates provide a quantitative means of evaluating energy losses, even
521
in nonequilibrium conditions, particularly important in modeling waves in complex bathymetries, in situations of mixed sea-swell, or when wave generation is taking place at very oblique angles to the coast, and in very shallow water where nonlinear fluxes can no longer maintain an equilibrium. Offshore and Coastal Tech., Inc., 911 Clay St., Vicksburg, MS 39180, USA. 88:3267 Sebekin, B.I., 1986. Influence of wave dispersion on directional tsunami propagation. Izv. Atmos. Ocean Phys. (a translation of Fiz. Atrnos. Okeana), 22(9):743-748. Inst. of Oceanol., Acad. of Sci., USSR. 88:3268 Slabakov, H.D., 1986. Assessment of the parameters of the autocorrelation and spectral functions of sea motion. Oceanology, Sofia, 16:74-83. (In Bulgarian, English abstract.) 88:3269 Smith, O.P., 1988. Duration of extreme wave conditions. J. WatWay Port coast. Ocean Engng, Am. Soc. cir. Engrs, 114(1):1-17. Statistical trends of the duration of extreme wave conditions, as characterized by hindcast wave information, are investigated at five sites along the U.S. coast. Identification of events and definition of their durations are based on a threshold for zero moment wave heights; the percentage exceedance above a specified threshold is roughly 30% of the average number of events per year, regardless of geographical location. The extremal type I distribution function is applied to model both the distribution of durations and of peak zero moment wave heights. The assumption of independence of duration from peak event intensity is proposed for estimating durations of zero moment wave heights above a threshold, given a peak zero moment wave height. 2130 Pony Farm Rd., Clayton, NC 27520, USA. 88:3270 Wtlbber, Chresten, 1986. [A numerical model for the investigation of baroclinic Rossby waves in the North Atlantic.] Bet. Inst. Meeresk. ChristianAlbrechts-Univ., 159:96pp. (In German, English abstract.) A linear, quasigeostrophic model describing windinduced, baroclinic Rossby waves in a closed basin is applied to the North Atlantic between 5 ° and 45°N, using the annual cycle of the wind stress curl as forcing function. Due to the large spatial scales of the wind field, Rossby waves are only generated