Mixing in the equatorial Pacific: the role of interleaving

University Of Hawaii, Honolulu

Investigators

Abstract

This project focuses on lateral mixing and the role of the observed interleaving of water masses across the equator. Estimates suggest that the interleaving has an effective lateral diffusion coefficient of the order of 1000 m2s-1. Imposing an enhanced mixing coefficient of this magnitude close to the equator is found in preliminary experiments with an ocean general circulation model (OGCM) to both limit the strength of the Equatorial Under Current (EUC) and reduce the cold bias in the eastern cold tongue, thus resolving two problems which plague ocean models used in climate studies. The ultimate goal is to provide a parameterization scheme for interleaving suitable for ocean models used in climate studies, and thus improves the reliability and predictive skill of climate models. An analysis of existing observations will be combined with linear stability theory, numerical process studies and an OGCM to elucidate the fundamental physics of the interleaving process. Associated fluxes of momentum and tracers will be quantified and the relationship between these fluxes and the broader scale characteristics of the ocean state will be determined. The main focus will be on inertial instability (and other shear induced instabilities) as the prime mechanism for the formation and subsequent evolution of the layering. Particular attention will be paid to the three dimensional nature of the interleaving process. Double diffusive vertical fluxes may also play a role and their impact will be investigated and quantified. A parameterization scheme for interleaving will be developed and tested, and its impact on the characteristics of an OGCM configured for the Pacific Ocean will be investigated. Broader Impacts: The usefulness of any climate forecast depends crucially on its skill and reliability; with implications for the way planners and resource managers react and the potential gains by human society. The reliability of a forecast is improved through an increased understanding of the physical processes involved. The enhanced mixing brought about by interleaving may well affect the development of ENSO events and possibly its decadal variability. The proposed work is designed to have an output that is directly useful to agencies charged with making ENSO forecasts, as well as other researchers. The work is directly related to the aims of the Climate variability and predictability Program (CLIVAR) and will be useful to the forthcoming ocean biogeochemistry program.