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- Author or Editor: J. V. Mansbridge x
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Abstract
Using a two-layer model of unstable shear flow, the transition from one dominant baroclinic wave to another is studied. This transition can be smooth, involving an intermediate mixed wave state, or abrupt, thereby displaying hysteresis. It is found that the transition is smooth when the beta effect is strong, and abrupt when it is weak.
Abstract
Using a two-layer model of unstable shear flow, the transition from one dominant baroclinic wave to another is studied. This transition can be smooth, involving an intermediate mixed wave state, or abrupt, thereby displaying hysteresis. It is found that the transition is smooth when the beta effect is strong, and abrupt when it is weak.
Abstract
Resonant interactions between a marginally unstable baroclinic wave and one or two pairs of neutral waves in a rotating, two-layer zonal Row model are studied. Analyses based on a multiple scaling technique are carried out for inviscid flow on a beta plane, inviscid flow on an f-plane, and slightly viscous flow on an f-plane. It is assumed that the neutral waves are of smaller order in amplitude than the unstable wave, and the flow domain is taken to be zonally periodic so that zonal wavelengths are discrete. In this and other respects, the theory differs from an earlier study by Loesch (1974a,b) and avoids a number of difficulties inherent in that work.
For an inviscid beta plane flow, the evolution of a wave triad is governed by a certain parameter N 2 N 3/U. If this is negative, the neutral waves are unable to grow substantially larger in amplitude than their respective initial amplitudes, despite which they have a disproportionately large effect on the evolution of the unstable wave. If O<N 2 N 3/U;<0.125, the neutral waves are largely unrestricted by their initial amplitudes and interact strongly with the unstable wave. Finally, if 0.125<N 2 N 3/U, all three waves grow rapidly without bound and the scaling assumption is soon violated.
For the flows on an f-plane, there exist two resonant triads with the unstable wave common to both. In this case, the neutral waves are always constrained by the size of their initial amplitudes. When the flow is inviscid, wave evolution is much the same as in the beta-plane problem with N 2 N 3/U≶0, whereas the addition of a small amount of viscosity results in the neutral waves being damped. There is no intermediate viscous regime in which the neutral waves are undamped, but “forget” their initial conditions.
Abstract
Resonant interactions between a marginally unstable baroclinic wave and one or two pairs of neutral waves in a rotating, two-layer zonal Row model are studied. Analyses based on a multiple scaling technique are carried out for inviscid flow on a beta plane, inviscid flow on an f-plane, and slightly viscous flow on an f-plane. It is assumed that the neutral waves are of smaller order in amplitude than the unstable wave, and the flow domain is taken to be zonally periodic so that zonal wavelengths are discrete. In this and other respects, the theory differs from an earlier study by Loesch (1974a,b) and avoids a number of difficulties inherent in that work.
For an inviscid beta plane flow, the evolution of a wave triad is governed by a certain parameter N 2 N 3/U. If this is negative, the neutral waves are unable to grow substantially larger in amplitude than their respective initial amplitudes, despite which they have a disproportionately large effect on the evolution of the unstable wave. If O<N 2 N 3/U;<0.125, the neutral waves are largely unrestricted by their initial amplitudes and interact strongly with the unstable wave. Finally, if 0.125<N 2 N 3/U, all three waves grow rapidly without bound and the scaling assumption is soon violated.
For the flows on an f-plane, there exist two resonant triads with the unstable wave common to both. In this case, the neutral waves are always constrained by the size of their initial amplitudes. When the flow is inviscid, wave evolution is much the same as in the beta-plane problem with N 2 N 3/U≶0, whereas the addition of a small amount of viscosity results in the neutral waves being damped. There is no intermediate viscous regime in which the neutral waves are undamped, but “forget” their initial conditions.
Abstract
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Abstract
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Abstract
Meridional heat transport in the North Pacific Ocean in a seasonally forced high-resolution global ocean general circulation model is compared to observations. At 24°N, annual mean heat transport in the model of 0.37×1011W is half the most recent direct estimate of 0.76±0.3×1015W from hydrographic data. The model value is low because the model ocean loses too little heat in the region of the Kuroshio Current Extension. The water ventilated in this region returns southward across 24°N at depth between 200 m and 500 m approximately 2°−4°C too warm. If the model surface temperature were relaxed to a temperature adjusted for the influence of persistent atmospheric cooling in this region, rather than relaxed to climatological sea surface temperature, the model heat transport would improve.
Assumptions inherent in estimating meridional heat transport from hydrographic sections are tested by examining the model. Rather than the abyssal circulation being steady, the model's deep western boundary currents vary seasonally to balance the seasonal cycle of Ekman transport, producing a larger seasonal variation in heat transport than is generally supposed for direct heat flux calculations. But the variability is such that there is no net contribution to the mean beat transport through a seasonal correlation between winds and surface temperature. The use of surface temperature observed during a single hydrographic section can seasonally bias an estimate of the wind-driven component of the beat transport, so a modification is proposed to the procedure by which compensation is made for seasonal variability in direct beat transport calculations. The most recent direct estimate was based on a springtime section, for which the model beat transport would be underestimated by about 0.05×1015W.
Interannual timescale correlations in the transport and temperature of the Kuroshio Current contribute a net southward transport of some 0.07×1015W. The role or simulated mesoscale eddies is minor.
Given the comparable order of the southward interannual heat transport and the northward seasonal bias, this present study does not suggest any significant revision to the latest direct heat transport estimate for 24°N in the Padfic.
Other features of the model general circulation are noted, including a Kuroshio Current transport that is stronger than observed and the persistence of a branch of the Kuroshio that does not separate at 35°N but continues close to the coast forming unrealistically deep mixed layers through intense surface cooling.
Abstract
Meridional heat transport in the North Pacific Ocean in a seasonally forced high-resolution global ocean general circulation model is compared to observations. At 24°N, annual mean heat transport in the model of 0.37×1011W is half the most recent direct estimate of 0.76±0.3×1015W from hydrographic data. The model value is low because the model ocean loses too little heat in the region of the Kuroshio Current Extension. The water ventilated in this region returns southward across 24°N at depth between 200 m and 500 m approximately 2°−4°C too warm. If the model surface temperature were relaxed to a temperature adjusted for the influence of persistent atmospheric cooling in this region, rather than relaxed to climatological sea surface temperature, the model heat transport would improve.
Assumptions inherent in estimating meridional heat transport from hydrographic sections are tested by examining the model. Rather than the abyssal circulation being steady, the model's deep western boundary currents vary seasonally to balance the seasonal cycle of Ekman transport, producing a larger seasonal variation in heat transport than is generally supposed for direct heat flux calculations. But the variability is such that there is no net contribution to the mean beat transport through a seasonal correlation between winds and surface temperature. The use of surface temperature observed during a single hydrographic section can seasonally bias an estimate of the wind-driven component of the beat transport, so a modification is proposed to the procedure by which compensation is made for seasonal variability in direct beat transport calculations. The most recent direct estimate was based on a springtime section, for which the model beat transport would be underestimated by about 0.05×1015W.
Interannual timescale correlations in the transport and temperature of the Kuroshio Current contribute a net southward transport of some 0.07×1015W. The role or simulated mesoscale eddies is minor.
Given the comparable order of the southward interannual heat transport and the northward seasonal bias, this present study does not suggest any significant revision to the latest direct heat transport estimate for 24°N in the Padfic.
Other features of the model general circulation are noted, including a Kuroshio Current transport that is stronger than observed and the persistence of a branch of the Kuroshio that does not separate at 35°N but continues close to the coast forming unrealistically deep mixed layers through intense surface cooling.
