The mixed-layer depth in the Ocean Model Intercomparison Project (OMIP): impact of resolving mesoscale eddies
<p>The ocean mixed layer is the interface between the ocean interior and the atmosphere or sea ice and plays a key role in climate variability. It is thus critical that numerical models used in climate studies are capable of a good representation of the mixed layer, especially its depth. Here...
| Main Authors: | , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-07-01
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| Series: | Geoscientific Model Development |
| Online Access: | https://gmd.copernicus.org/articles/16/3849/2023/gmd-16-3849-2023.pdf |
| Summary: | <p>The ocean mixed layer is the interface between the ocean interior and the atmosphere or sea ice and plays a key role in climate variability. It is
thus critical that numerical models used in climate studies are capable of a good representation of the mixed layer, especially its depth. Here we
evaluate the mixed-layer depth (MLD) in six pairs of non-eddying (1<span class="inline-formula"><sup>∘</sup></span> grid spacing) and eddy-rich (up to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1</mn><mo>/</mo><mn mathvariant="normal">16</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="22a3600bd5eb5cb9a3249b3a22652254"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gmd-16-3849-2023-ie00001.svg" width="27pt" height="14pt" src="gmd-16-3849-2023-ie00001.png"/></svg:svg></span></span><span class="inline-formula"><sup>∘</sup></span>) models from the
Ocean Model Intercomparison Project (OMIP), forced by a common atmospheric state. For model evaluation, we use an updated MLD dataset computed from
observations using the OMIP protocol (a constant density threshold). In winter, low-resolution models exhibit large biases in the deep-water
formation regions. These biases are reduced in eddy-rich models but not uniformly across models and regions. The improvement is most noticeable in
the mode-water formation regions of the Northern Hemisphere. Results in the Southern Ocean are more contrasted, with biases of either sign remaining
at high resolution. In eddy-rich models, mesoscale eddies control the spatial variability in MLD in winter. Contrary to a hypothesis that the
deepening of the mixed layer in anticyclones would make the MLD larger globally, eddy-rich models tend to have a shallower mixed layer at most
latitudes than coarser models do. In addition, our study highlights the sensitivity of the MLD computation to the choice of a reference level and
the spatio-temporal sampling, which motivates new recommendations for MLD computation in future model intercomparison projects.</p> |
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| ISSN: | 1991-959X 1991-9603 |