Numerical Mixing Suppresses Submesoscale Baroclinic Instabilities Over Sloping Bathymetry
Abstract The impacts of spurious numerical salinity mixing Mnum on the larger‐scale flow and tracer fields are characterized using idealized simulations. The idealized model is motivated by realistic simulations of the Texas‐Louisiana shelf and features oscillatory near‐inertial wind forcing. Mnum c...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
American Geophysical Union (AGU)
2024-12-01
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| Series: | Journal of Advances in Modeling Earth Systems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2024MS004321 |
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| Summary: | Abstract The impacts of spurious numerical salinity mixing Mnum on the larger‐scale flow and tracer fields are characterized using idealized simulations. The idealized model is motivated by realistic simulations of the Texas‐Louisiana shelf and features oscillatory near‐inertial wind forcing. Mnum can exceed the physical mixing from the turbulence closure Mphy in frontal zones and within the mixed layer. This suggests that simulated mixing processes in frontal zones are driven largely by Mnum. Near‐inertial alongshore wind stress amplitude is varied to identify a base case that maximizes the ratio of Mnum to Mphy in simulations with no prescribed horizontal mixing. We then test the sensitivity of the base case with three tracer advection schemes (MPDATA, U3HC4, and HSIMT) and conduct ensemble runs with perturbed bathymetry. Instability growth is evaluated using the volume‐integrated eddy kinetic energy (EKE) and available potential energy (APE). While all schemes have similar total mixing, the HSIMT simulations have over double the volume‐integrated Mnum and 20% less Mphy relative to other schemes, which suppresses the release of APE and reduces the EKE by roughly 25%. This results in reduced isohaline variability and steeper isopycnals, evidence that enhanced Mnum suppresses instability growth. Differences in EKE and APE between the MPDATA and U3HC4 simulations are marginal. However, the U3HC4 simulations have 25% more Mnum. Experiments with variable horizontal viscosity and diffusivity coefficients show that small amounts of prescribed horizontal mixing improve the representation of the ocean state for all advection schemes by reducing the Mnum and increasing the EKE. |
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| ISSN: | 1942-2466 |