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Motivation
Ocean models that use eulerian vertical coordinates, i.e. geopotential and terrain-following level models, cannot preserve the adiabatic properties of an advected water parcel. This results in a spurious diapycnal mixing that can irreversibly and unrealistically mix the simulated water masses.
Objectives
This study aims to document and quantify the numerically-induced mixing in 'fixed' coordinate models (i.e., ROMS, MITgcm; σ- levels and z- respectively) for idealized scenarios: a gravitational adjustment and a pure propagating internal wave field.
Results
The Gravitational Adjustment scenario
The gravitational adjustment is a classic scenario used to assess model advection scheme performances. Here we followed the configuration used by Haidvogel and Beckmann (1999) and reprodeuced more recently by Burchard and Rennau (2009) for 3 different models: HYCOM, ROMS and the MITgcm. Movies of tis scenario are seen below.
Lock exchange with HYCOM z-mode, 2nd order for momentum advection and FCT2 for tracer advection, Δx=0.5km, 40 z-levels
Lock exchange with ROMS, 3rd order for momentum advection and also the for tracer advection, Δx=0.5km, 40 σ-levels
Lock exchange with MITgcm, Adams-Bashfort for momentum advection and 3rd order DST the for tracer advection, Δx=0.5km, 40 z-levels
The Internal Wave scenario
Research Team
Dr. E. Chassignet , Professor, Director of COAPS
F. Gouillon , Post-Doc
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"Either you decide to stay in the shallow end of the pool or you go out in the ocean" C. Reeve
Center for Ocean Atmospheric Prediction Studies
Florida State University
200 R.M. Johnson Bldg, Tallahassee, FL, 32306-2840
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