Southern Ocean Uptake in the MPAS-Ocean Model

• Main Authors: Large, William G., Ringler, Todd
• Language: unknown
• Published: 2019
• Subjects: 58 GEOSCIENCES; Southern Ocean; Indian; Langmuir
• Online Access: http://www.osti.gov/servlets/purl/1480355; https://www.osti.gov/biblio/1480355; https://doi.org/10.2172/1480355

The research added to the understanding of Southern Ocean Uptake in the following ways. 1) No single process in the model could be “tuned” to improve Southern Ocean uptake of heat, CO 2 and CFCs. 2) More comprehensive studies revealed that multiple aspects of the model are important; in particular the general circulation control of deep (>200m) stratification (Small et al., 2019) and salinity contributions to the shallow (< 200 m) stratification (DuVivier et al, 2018). These two aspects are not strongly connected. The first can be very much improved by increasing horizontal resolution, primarily because of more transport of high salinity water from the Indian Ocean into the Southern Ocean south of Africa, so we now know that “parameterizing” this salinity source will be one necessary step to improving the Southern Ocean uptake at low resolution. 3) However, the second was found to be more than just a resolution issue, which may explain why many studies have found that higher resolution improves only some aspects of model solutions, but degrades others. Even in cases where the surface wind is too strong, the shallow stratification is sufficient to inhibit vertical mixing even though the salinity stabilization is weak compared to observations. The conclusion is that the process responsible for mixing through the stable salinity barrier above 200m is missing from the model. Therefore, a second necessary step is to find the process then incorporate it into the model. The project focused on ocean surface wave driven Langmuir turbulence as the source of additional mixing by studying Large Eddy Simulations (LES) of Southern Ocean boundary layers as they eroded a realistic salinity barrier. The wind, buoyancy and wave driven boundary layer turbulence was found to be well described by Monin-Obukhov similarity by developing similarity functions of the wave driving, and combining these with the established wind and buoyancy functions (Large et al., 2018a). These functions and a novel analysis of the momentum flux and ...