Nonlinearly forced equatorial deep jets
The response of the Miami Isopycnic Coordinate Ocean Model (MICOM) in an idealized equatorial ocean basin is evaluated using the response of the Modular Ocean Model (MOM), which has a long history of successful equatorial simulations, as a baseline. The inclusion of diapycnal diffusion (optional in the MICOM, but required in the MOM) substantially alters the character of the equatorial current and density structures simulated by the MICOM, and brings the response of the two models into reasonable agreement. This result gives confidence that the MICOM is an adequate equatorial modeling tool for the second part of this study. The principle changes in the MICOM's response induced by the inclusion of diapycnal diffusion are: (1) the undercurrent is extended over the entire width of the basin; (2) the surface zonal and meridional density-gradients near the equator are strengthened; and (3) the peak buoyancy-frequency is reduced to physically reasonable values. The remaining differences between the responses of the two models are traced largely to the MOM's convective adjustment scheme which only homogenizes thermodynamic properties as opposed to the MICOM's which also homogenizes momentum. This result indicates that convective adjustment plays a substantial role in determining the character of near-surface flow whenever downgradient advection of density takes place in the mixed layer.^ A MICOM simulation of a highly resolved, very low dissipation, idealized sub-thermocline equatorial ocean of 15$\sp\circ$ zonal extent forced at the surface by a surface stress characterized by high horizontal wavenumber and high frequency variability is used to test the hypothesis that the Equatorial Deep Jets are forced by nonlinear processes. The model response, which bears a quantitative resemblance to observations of the Pacific Equatorial Deep Jets when scaled to account for the truncated zonal extent of the basin, is essentially composed of a set of first meridional mode Rossby waves of approximately basin-scale zonal wavelength. These waves are forced in the upper ocean by nonlinear processes that are hypothesized to be a combination of an equatorial analog of geostrophic-turbulence and resonant wave-wave interactions. ^
George Dail Rowe,
"Nonlinearly forced equatorial deep jets"
Dissertations and Master's Theses (Campus Access).