Wave-Mean Flow Interactions in the Equatorial Ocean

McPhaden, Michael J.; Ripa, P.

doi:10.1146/annurev.fl.22.010190.001123

Cited by 24 publications

(5 citation statements)

References 73 publications

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“…Thus, both kinds of wave signals in the delayed-oscillator paradigm are influenced by the shift, because they are being forced and propagating under different seasonal mean conditions. These arguments are consistent with several previous studies on how features of the equatorial Pacific mean state can affect equatorially trapped, low-frequency baroclinic Kelvin and Rossby waves (e.g., McPhaden and Ripa 1990;Giese and Harrison 1990;Long and Chang 1990;Zheng et al 1998). The seasonal variation in major equatorial currents in the upper ocean and the equatorial thermocline slope continuously affects equatorial waves excited by ENSO wind anomalies.…”

Section: Discussionsupporting

confidence: 93%

Correlative Evolutions of ENSO and the Seasonal Cycle in the Tropical Pacific Ocean

Xiao

Mechoso

2009

Journal of the Atmospheric Sciences

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This study examines whether shifts between the correlative evolutions of ENSO and the seasonal cycle in the tropical Pacific Ocean can produce effects that are large enough to alter the evolution of the coupled atmosphere-ocean system. The approach is based on experiments with an ocean general circulation model (OGCM) of the Pacific basin, in which the seasonal and nonseasonal (interannually varying) components of the surface forcing are prescribed with different shifts in time. The shift would make no difference in terms of ENSO variability if the system were linear. The surface fluxes of heat and momentum used to force the ocean are taken from 1) simulations in which the OGCM coupled to an atmospheric GCM produces realistic ENSO variability and 2) NCEP reanalysis data corrected by Comprehensive Ocean-Atmosphere Data Set climatology for the 20-yr period 1980-99. It is found that the response to the shifts in terms of eastern basin heat content can be 20%-40% of the maximum interannual anomaly in the first experiment, whereas it is 10%-20% in the second experiment. In addition, the response to the shift is event dependent. A response of this magnitude can potentially generate coupled atmosphere-ocean interactions that alter subsequent event evolution. Analysis of a selected event shows that the major contribution to the response is provided by the anomalous zonal advection of seasonal mean temperature in the equatorial band. Additional OGCM experiments suggest that both directly forced and delayed signals provide comparable contributions to the response. An interpretation of the results based on the ''delayed oscillator'' paradigm and on equatorial wave-mean flow interaction is given. It is argued that the same oceanic ENSO anomalies in different times of the oceanic seasonal cycle can result in different ENSO evolutions because of nonlinear interactions between equatorially trapped waves at work during ENSO and the seasonally varying upper-ocean currents and thermocline structure.

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Section: Discussionsupporting

confidence: 93%

Correlative Evolutions of ENSO and the Seasonal Cycle in the Tropical Pacific Ocean

Xiao

Mechoso

2009

Journal of the Atmospheric Sciences

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“…[41] It is of interest to compare our results with the studies of the effect of zonal currents on surface equatorial Kelvin waves – waves that are usually associated with anomalies in surface wind stress and penetrate the entire depth of the ocean [cf., McPhaden and Ripa , 1990 ; Wang , 2003 ]. Like (5), these equatorially trapped waves propagate eastward and their meridional velocity vanishes everywhere.…”

Section: Discussionmentioning

confidence: 99%

Instability of some equatorially trapped waves

2013

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“…Consider any x-independent basic flow and an O (a) perturbation, where it is formally assumed that a → 0. The total streamfunction can be expanded as McPhaden & Ripa 1990;Ripa 1992b). The first term represents the prescribed basic flow (which is a trivial nonlinear solution of the equations of motion, because it is x-and t-independent).…”

Section: Energeticsmentioning

confidence: 99%

Baroclinic instability in a reduced gravity, three-dimensional, quasi-geostrophic model

Ripa

2000

J. Fluid Mech.

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The classical quasi-geostrophic model in an active layer with an arbitrary vertical structure is modified by adding a boundary condition at the interface with a passive (motionless) lower layer: the difference between isopycnal and interface elevations is a Lagrangian constant, so that a particle in this boundary remains there and conserves its density. The new model has the appropriate integrals of motion: in particular, a free energy quadratic and positive definite in the deviation from a state with a uniform flow, made up of the internal and ‘external’ potential energies (due to the displacement of the isopycnals and the interface) and the kinetic energy.Eady's model of baroclinic instability is extended with the present system, i.e. including the effect of the free lower boundary. The integrals of motion give instability conditions that are both necessary and sufficient. If the geostrophic slope of the interface is such that density increases in opposite directions at the top and bottom boundaries, then the basic flow is nonlinearly stable. For very weak internal stratification (as compared with the density jump at the interface) normal modes instability is similar to that of a simpler model, with a rigid but sloping bottom. For stronger stratification, though, the deformation of the lower boundary by the perturbation field also plays an important role, as shown in the dispersion relation, the structure of growing perturbations, and the energetics of the instability. The energy of long growing perturbations is mostly internal potential, whereas short ones have an important fraction of kinetic energy and, for strong enough stratification, external potential.

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Wave-Mean Flow Interactions in the Equatorial Ocean

Cited by 24 publications

References 73 publications

Correlative Evolutions of ENSO and the Seasonal Cycle in the Tropical Pacific Ocean

Correlative Evolutions of ENSO and the Seasonal Cycle in the Tropical Pacific Ocean

Instability of some equatorially trapped waves

Baroclinic instability in a reduced gravity, three-dimensional, quasi-geostrophic model

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