# Yann-Treden Tranchant: Unrealistic submesoscales and artificial mixing in ocean models

**URL:** <https://forum.access-hive.org.au/t/yann-treden-tranchant-unrealistic-submesoscales-and-artificial-mixing-in-ocean-models/7243>\
**Category:** COSIMA/Cryosphere Workshop 2026 Lightning Talks\
**Created:** [5 November 2026 22:10 UTC](https://forum.access-hive.org.au/t/yann-treden-tranchant-unrealistic-submesoscales-and-artificial-mixing-in-ocean-models/7243 "2026-11-05T22:10:47Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![lachlanswhyborn](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.access-hive.org.au/lachlanswhyborn/32/1837_2.png) [@lachlanswhyborn](https://forum.access-hive.org.au/u/lachlanswhyborn)\
**Post date:** [5 November 2026 22:10 UTC](https://forum.access-hive.org.au/t/yann-treden-tranchant-unrealistic-submesoscales-and-artificial-mixing-in-ocean-models/7243/1 "2026-11-05T22:10:47Z")

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Yann-Treden Tranchant: Unrealistic submesoscales and artificial mixing in ocean models

The growing use of kilometre-scale ocean models, together with new high-resolution observations from the Surface Water and Ocean Topography (SWOT) mission, provides new opportunities to study submesoscale dynamics and their role in vertical heat and tracer fluxes.

Here, we use a kilometre-scale regional model to investigate how vertical discretization and momentum closure control numerical mixing and the representation of interior ocean dynamics in a meander of the Antarctic Circumpolar Current. We show that the vertical resolution needed to suppress grid-scale noise depends strongly on stratification, in agreement with recently proposed criterion. We further show that, for a similar number of vertical levels, a stratification-aware vertical grid strongly reduces numerical instabilities compared with a conventional grid.

Because very fine vertical resolution can become too expensive at kilometre and sub-kilometre horizontal resolution, we also introduce and evaluate a wave-dissipation momentum closure. This scheme suppresses spurious divergent grid-scale modes while preserving the resolved submesoscale dynamics.

When these numerical instabilities are not controlled, enhanced diapycnal mixing erodes stratification, weakens mesoscale buoyancy gradients and fronts, and artificially increases small-scale variability and vertical fluxes. Combining stratification-aware vertical discretization with targeted wave dissipation therefore provides a practical way to set up submesoscale-resolving models that maintain realistic interior dynamics while limiting numerical diapycnal mixing.