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Improved Equatorial Upper Ocean Vertical Mixing in the NOAA/GFDL OM4 Model
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  • Brandon G Reichl,
  • Andrew T. Wittenberg,
  • Stephen M Griffies,
  • Alistair Adcroft
Brandon G Reichl
NOAA, GFDL

Corresponding Author:[email protected]

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Andrew T. Wittenberg
NOAA Geophysical Fluid Dynamics Laboratory
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Stephen M Griffies
GFDL, NOAA
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Alistair Adcroft
Princeton University
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Abstract

Deficiencies in upper ocean vertical mixing parameterizations contribute to tropical upper ocean biases in global coupled general circulation models, affecting their simulated ocean heat uptake and ENSO variability. To better understand these deficiencies, we develop a suite of ocean model experiments including both idealized single column models and realistic global simulations. The vertical mixing parameterizations are first evaluated using large eddy simulations as a baseline to assess uncertainties and evaluate their implied turbulent mixing. Global models are then developed following NOAA/GFDLâ\euro™s 0.25$\degree$ nominal ocean horizontal grid spacing OM4 (uncoupled ocean) configuration of the MOM6 ocean model, with various modifications that target improvements to biases in the original model. We identify a variety of enhancements to the existing mixing schemes that are evaluated using observational constraints from TAO moorings and Argo floats. In particular, we find that we can improve the diurnal variability of mixing in OM4 via modifications to its mixing scheme, and that we can improve the net mixing in the upper thermocline by reducing the background vertical viscosity, allowing for more realistic, less diffuse currents. The improved OM4 model better represents the mixing and its diurnal deep-cycle variability, leading to more realistic time-mean tropical thermocline structure, mixed layer depths, SSTs, and a better Pacific Equatorial Undercurrent.
09 Feb 2024Submitted to ESS Open Archive
13 Feb 2024Published in ESS Open Archive