Dennis W. Moore

Sverdrup and Nonlinear Dynamics of the Pacific Equatorial Currents

Abstract The Sverdrup circulation in the tropical Pacific is constructed from satellite scatterometer winds, compared with measured ocean currents, and diagnosed in an ocean GCM. Previous depictions of the Sverdrup circulation near the equator have shown only weak vertically integrated flows; here it is shown that the actual transports are not weak. This discrepancy could be due either to inaccuracies in the wind forcing or to Sverdrup dynamics being too simple in this region. Scatterometer winds show a strip of positive curl along the SST front north of the equator in the eastern Pacific that is due to wind speed changes induced by the front. Including that additional element of curl forcing greatly improves the realism of the Sverdrup representation, but the magnitudes of the equatorial transport are still too small by a factor of about 2. Although the nonlinear (advective and friction) terms are small in the model momentum balance, they are O(1) in the vorticity balance, especially because their meridi...

The Pacific Subsurface Countercurrents and an Inertial Model

Abstract The Tsuchiya jets, or subsurface countercurrents, extend across the Pacific Ocean carrying 7 (±2) × 106 m3 s−1 eastward on each side of the equator. Mean meridional sections of potential temperature, salinity, neutral density anomaly, and the square of buoyancy frequency are presented for the western, central, and eastern tropical Pacific Ocean. These sections are used together with maps of depth and salinity on isopycnals, as well as thickness between isopycnals, to describe the evolution of the Tsuchiya jets as they flow from west to east. An inertial-jet model is formulated in which conservation of the Bernoulli function and potential vorticity combine with the eastward shoaling of the tropical pycnocline to dictate the jet structure. This model jet is consistent with a number of features of the Tsuchiya jets: their roughly constant volume transports, their advection of properties such as salinity and oxygen over long zonal distances, their rapidity and narrowness, their poleward shift from we...

Temporal and Spatial Structure of the Equatorial Deep Jets in the Pacific Ocean

Abstract The spatial and temporal structure of the equatorial deep jets (EDJs) in the Pacific Ocean is investigated using CTD station data taken on the equator from 1979 through 2001. The EDJs are revealed in profiles of vertical strain, ξz, estimated from the CTD data in a stretched vertical coordinate system. The majority of synoptic meridional sections were occupied over an 8-yr span west of the date line. Two-decade equatorial time series are available at both 110°W and 140°W. Analysis shows the expected equatorial trapping of ξz but yields little new detailed information about the EDJ meridional structure. Analysis of the equatorial data yields novel results. The EDJs are most easily seen in the eastern Pacific (at and east of 140°W). There, they may be isolated from the influence of higher-frequency Rossby waves generated by surface forcing. Spectral analysis of equatorial ξz profiles shows a significant and coherent peak at 400-sdbar vertical wavelength (with No = 1.56 × 10−3 s−1) from 95°W to 142°...

Interior Reflections of a Periodically Forced Equatorial Kelvin Wave

Abstract A fully three-dimensional, wind-forced equatorial model is used to study the effects of the strong near- surface equatorial pycnocline on energy transmission into the deep ocean. The equatorial Kelvin waves forced by a patch of zonal wind oscillating at the annual period are isolated from the complete response, and their energy transmission into the deep ocean is investigated as a function of forcing geometry, pycnocline structure, and the amplitude of deep-ocean mixing. Solutions form well-defined beams of energy that propagate through realistic pycnoclines with surprisingly little reflection. Vertical mixing damps the beams in the direction of their propagation and stretches their longitudinal extent. For sufficiently strong mixing the solutions low their beamline character and appear as surface-trapped signals. This result may help to resolve the differences between the solutions found in previous investigations.

Evolution of mixed Rossby gravity waves

A Greens function is derived, which can be used to study and predict the evolution of the velocity and pressure fields associated with the mixed Rossby gravity wave component of the totality of motions due to forcing on an equatorial β plane. Initial value problems can also be solved with the aid of the Greens function. Since energy associated with the Rossby gravity mode always travels east, the Greens function can be employed to predict what signal should arrive to the east of a given location if the time history of the fields are known at that position. Various simple analytical examples are discussed. A numerical ocean general circulation model is used to demonstrate the usefulness of the Greens function formalism.

Validating the NSCAT winds in the vicinity of the Pacific intertropical convergence zone

It is known that the NSCAT winds are influenced by precipitation, and so are potentially in error in regions of high rainfall, such as the Pacific ITCZ. We assess this potential error by comparing NSCAT winds to other products and by determining the possible impact on modeling the Pacific NECC. In the latitude band of the ITCZ, there are large differences between wind products from the ECMWF and NSCAT. A comparison with TAO buoy winds shows a bias of NSCAT data towards a higher zonal wind stress at 8°N. The spatial distribution of this bias distorts the Ekman pumping velocity across the ITCZ, and results in a NECC that is 0.1-0.2 m/s weaker than that forced by the ECMWF winds. This is not a trivial amount during the spring, when the strength of the NECC in the eastern Pacific is of the same magnitude.

Exact Solutions to Kawase's Linear Model of Deep Ocean Circulation

Abstract Exact solutions are found for Kawases linear, two-layer model of mass-driven deep-ocean circulation. It is demonstrated that for strong damping, even though the deep western boundary current (DWBC) bifurcates at the equator as found in Kawases perturbation solution, the equatorial flow is much weaker and has a much broader scale than the imposed DWBC. It is found that the presence of an eastern boundary is not necessary for the DWBC to cross the equator in the weak damping case.