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Data Assimilation Seminar Series

Prof. Yusuke Uchiyama (Nov. 17, 2017, 15:30-)

Affiliation Department of Civil Engineering, Kobe University
Title Challenges and issues in forward regional ocean modeling: Eddies, terrestrial influences, and surface gravity waves
Abstract Regional downscaling oceanic modeling has substantially been progressed in terms of the model physics and numeric in the last decades. State-of-the-art models enable us to convey basin-scale oceanic information to nearshore and marginal seas at significantly finer grid resolution, allowing mesoscale and submesoscale eddy resolving simulations with realistically considering terrestrial freshwater input, tides, surface wind and atmospheric forcing, and even surface gravity waves, for practical and operational purposes. I will principally introduce a couple of forward modeling projects at Kobe University based on the Regional Oceanic Modeling System (ROMS). The first topic is on the reproducibility of the Kuroshio that largely affects the marine and atmospheric environment along the Pacific coast of Japan. The Kuroshio is well reproduced with submesoscale eddy resolving ROMS configuration even without assimilation, while coarser resolution forward models fail with unrealistically energetic meandered path, suggesting that the appropriate energy dissipation relying on submesoscale structure leads to adequate stabilization of the Kuroshio. Such small-scale eddies are ubiquitous in nature and in fine-resolution models, whereas they are pronouncedly affected by surface gravity waves. Another example is a double nested Seto Inland Sea model, where 3DVAR and LETKF are experimentally introduced. Although the assimilations improve the model reproducibility, proper buoyancy inputs through rivers are essential to correct salinity biases. A take-home message is that careful and reliable forward modeling is solidly requisite a priori for unbiased, successful oceanic data assimilation.
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