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The three-dimensional ocean circulation: Lagrangian diagnostics based on General Circulation Model results
Bruno Blanke, Sabrina Speich
Laboratoire de Physique des Océans
blanke@univ-brest.fr(Abstract received 05/03/2005 for session B)
ABSTRACT
We point here a general question that arises in Physical Oceanography: where do water masses come from and where are they going? Pathways and mechanisms for oceanic heat and fresh water transports are critical issues in the understanding of the present climate and its stability. Indeed, the ocean circulation transfers heat and fresh water between different climate regimes and between different ocean basins. On regional scales, e.g., eastern boundary current systems, water mass transfers are also worth studying to understand the complexity of the connections achieved between the coastal and open oceans. Transports and pathways are often inferred by merging distinct (mostly Eulerian) sources of data and matching available pieces of knowledge on a basin or global scale. Yet, the most natural approach to estimate flows' origins and pathways is to follow the movement of water masses and their transformation. In this talk we will show quantitative and qualitative information about the ocean dynamics calculated by the Lagrangian analysis of high performance ocean models. The accent will be put on large-scale diagnostics aiming at characterizing the various branches of the thermohaline circulation as well as on connections established on a regional scale. Our Lagrangian diagnostics rest on the injection of fictitious particles in the time varying, three-dimensional velocity field of a general circulation model. Trajectories are computed with an appropriate scheme that fully respects the local non-divergence of the flow. Quantitative results are obtained by increasing considerably the number of particles. As a current may be entirely determined from the particles that compose it, with well-defined characteristics (position, velocity, and other scalars), the transport of a given water mass can be computed from its own particles and their associated infinitesimal transport.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005