A Gradient Based Subgrid‐Scale Parameterization for Ocean Mesoscale Eddies

Journal Article · Thu Jan 26 00:00:00 EST 2023 · Journal of Advances in Modeling Earth Systems

DOI:https://doi.org/10.1029/2022MS003356· OSTI ID:1922121

Khani, Sina  ^[1]; Dawson, Clinton N. ^[1]

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1. Oden Institute for Computational Engineering and Sciences University of Texas Austin TX USA

Abstract Mesoscale eddies play an important role in transport of heat and biogeochemical tracers in the global ocean circulation. Resolving these energetic eddies, however, is challenging in ocean general circulation models (OGCM) because it requires a horizontal grid spacing of ≲1/8° that is computationally expensive. As a result, we are required to parameterize mesoscale eddy effects on large‐scale ocean flows. In this work, we introduce a new subgrid‐scale (SGS) model that is developed based on a Taylor series expansion of resolved variables to parameterize subgrid mesoscale eddy transports and momentum fluxes in OGCM. We have performed an a priori study to evaluate the performance of our new gradient model using high‐resolution ocean simulations. Our results show that the gradient model well predicts the actual SGS thickness fluxes in the zonal and meridional directions in coarse‐resolution simulations with the grid spacing ≳1/4°. The unresolved kinetic energy at the ocean surface is also skillfully estimated. More importantly, unlike current mesoscale eddy parameterizations, which are mainly developed based on an assumption of flat bottom ocean, our new SGS model can capture the structure of unresolved standing meanders at the ocean surface. We have also developed a dynamic procedure for setting in non‐dimensional parameters in our new parameterization through a non‐ad hoc and tuning‐free method. Overall, this work suggests that implementing the gradient model in OGCM can improve the model accuracy with an affordable computational cost in eddy‐permitting and non‐eddying simulations.

• Sponsoring Organization: USDOE
• Grant/Contract Number: DE‐SC‐0022211
• OSTI ID: 1922121
• Alternate ID(s): OSTI ID: 1923927
• Journal Information: Journal of Advances in Modeling Earth Systems, Journal Name: Journal of Advances in Modeling Earth Systems Vol. 15 Journal Issue: 2; ISSN 1942-2466
• Publisher: American Geophysical Union (AGU)
• Country of Publication: United States
• Language: English