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Ocean eddies, fronts, and air-sea exchanges: Observations and high resolution simulations
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Global ocean modeling at kilometer scale mesh resolution for studying ocean eddies, fronts, and air-sea exchanges (Invited)
Wednesday 9th @ 1530-1550, Conference Room 4
Dimitris Menemenlis* , California Institute of Technology
Presenter Email: menemenlis@me.com |
| Global, eddying numerical ocean simulations started to become computationally feasible some twenty years ago. In these early computations, carried out with 15-25-km horizontal grid spacing, the impact of tides on ocean transport and mixing was represented implicitly, e.g., by vertical diffusivity and viscosity coefficients. More recent computations, with horizontal grid spacing of 10 km or less, started to admit the gravest modes of the internal gravity wave spectrum. This spurred the development of simulations that are forced simultaneously by atmospheric fields and tides. The horizontally and time-varying stratification in these combined ocean circulation and tides simulations lead to a better representation of internal tides. Conversely, the inclusion of tides lead to more accurate description of ocean transport and mixing.
The Estimating the Circulation and Climate of the Ocean (ECCO) consortium recently used the Massachusetts Institute of Technology general circulation model (MITgcm) to carry out a global, kilometer-scale ocean simulation that includes sea-ice and tidal excitation, and that spans scales from planetary gyres to internal tides. This km-scale simulation is a virtual ocean that admits submesoscale and internal waves dynamics not normally represented in global calculations, extending simulated ocean behavior beyond broadly quasi-geostrophic flows and providing a preliminary example of a next-generation computational approach to explicitly probe the interactions between dominant energetic scales in the ocean and instabilities that are usually parameterized. Early science studies based on the ECCO/MITgcm km-scale simulation demonstrate the importance of resolving, on global scales, fine-scale ocean variability. In particular, fine scale ocean variability has significant impacts on air-sea exchanges and on vertical transports of heat and chemical properties in the upper ocean. These early studies reinforce the notion that resolving eddies and tides and admitting sub-mesoscale processes in numerical ocean models will lead to a significant boost in climate-model skill. |
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