Impacts of regional mixing on the temperature structure of the equatorial Pacific Ocean. Part 1: Vertically uniform vertical diffusion

Abstract

a b s t r a c tWe investigate the sensitivity of numerical-model solutions to regional changes in vertical diffusion. Specifically, we vary the background diffusion coefficient, κ b , within spatially distinct subregions of the tropical Pacific, assess the impacts of those changes, and diagnose the processes that account for them.Solutions respond to a diffusion anomaly, δκ b , in three ways. Initially, there is a fast response (several months), due to the interaction of rapidly-propagating, barotropic and gravity waves with eddies and other mesoscale features. It is followed by a local response (roughly one year), the initial growth and spatial pattern of which can be explained by one-dimensional (vertical) diffusion. At this stage, temperature and salinity anomalies are generated that are either associated with a change in density ("dynamical" anomalies) or without one ("spiciness" anomalies). In a final adjustment stage, the dynamical and spiciness anomalies spread to remote regions by radiation of Rossby and Kelvin waves and by advection, respectively.In near-equilibrium solutions, dynamical anomalies are generally much larger in the latitude band of the forcing, but the impact of off-equatorial forcing by δκ b on the equatorial temperature structure is still significant. Spiciness anomalies spread equatorward within the pycnocline, where they are carried to the equator as part of the subsurface branch of the Pacific Subtropical Cells, and spiciness also extends to the equator via western-boundary currents. Forcing near and at the equator generates strong dynamical anomalies, and sometimes additional spiciness anomalies, at pycnocline depths. The total response of the equatorial temperature structure to δκ b in various regions depends on the strength and spatial pattern of the generation of each signal within the forcing region as well as on the processes of its spreading to the equator.

An Increase of the Indonesian Throughflow by Internal Tidal Mixing in a High‐Resolution Quasi‐Global Ocean Simulation

“…However, we find these changes in SSH not to be associated with some specific island chain (e.g., Caroline Islands at 137°-153°E and Marshall Islands at 165°-172°E). This result suggests that the impacts of localized tidal mixing, such as around islands chains, spread all over the basin via Rossby and Kelvin waves as suggested by Furue et al (2015).…”

Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

“…Previous studies have documented several processes of wave dissipation which operate through nonlinearities in the momentum equations (e.g., baroclinic instability and subsequent breaking of the wave, LaCasce and Pedlosky []), momentum diffusion toward the eddy field [ Qiu et al ., ], and wave triad instability [ Qiu et al ., ]. Other studies have focused on the effect of temperature‐diapycnal diffusion on the wave amplitude attenuation [ Marchal , ; Furue et al ., ], which is more relevant for the interpretation of our results considering that the vertical flux in LIN (i.e., without nonlinearities in the momentum equations) yields comparable features than CR (see below). In particular, the theoretical study by Marchal [] indicates that vertical diffusion can critically damp the Rossby waves in the longwave limit, with the decay rate increasing linearly with the square root of vertical diffusivity.…”

An Evaluation of the Large-Scale Implementation of Ocean Thermal Energy Conversion (OTEC) Using an Ocean General Circulation Model with Low-Complexity Atmospheric Feedback Effects

“…The adjustment process towards a new balance involves the generation and propagation of particular types of ocean waves, such as Rossby waves, and equatorial and coastal Kelvin waves. These waves spread the [33]) are also shown: dynamical (middle) and spiciness (lower). Color scale is the same as in Figure 4.…”

“…Since potential density is a function of temperature and salinity, this would also mean that anomalies of opposite signs across the discharge depth would also emerge in the temperature and salinity fields. [33]) are also shown: dynamical (middle) and spiciness (lower). Color scale is the same as in Figure 4.…”

“…Temperature and salinity anomalies can also be advected by the flow field in the same way as passive tracers; this occurs when the two properties happen to vary in a compensating manner, for example from warm and salty to cold and fresh, such that they do not result in a change in potential density. Furue et al give details on how to separate δT into a wave component (dynamical anomaly) and an advective component (spiciness anomaly) [33], and provide examples on how they propagate in the tropical Pacific. These components are displayed in the middle and lower panels of Figures 5 and 6.…”