The mixed-layer depth in the Ocean Model Intercomparison Project (OMIP): impact of resolving mesoscale eddies

• Published in: Geoscientific Model Development
• Main Authors: Treguier, Anne, Marie, de Boyer Montégut, Clement, Bozec, Alexandra, Chassignet, Eric, P, Fox-Kemper, Baylor, Mcc. Hogg, Andy, Iovino, Doroteaciro, Kiss, Andrew, E, Le Sommer, Julien, Li, Yiwen, Lin, Pengfei, Lique, Camille, Liu, Hailong, Serazin, Guillaume, Sidorenko, Dmitry, Wang, Qiang, Xu, Xiaobio, Yeager, Steve
• Other Authors: Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDE]Environmental Sciences; [SDU]Sciences of the Universe [physics]; Southern Ocean; Sea ice
• Online Access: https://hal.science/hal-04284486; https://hal.science/hal-04284486/document; https://hal.science/hal-04284486/file/gmd-16-3849-2023.pdf; https://doi.org/10.5194/gmd-16-3849-2023

International audience Abstract. 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∘ grid spacing) and eddy-rich (up to 1/16∘) 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.