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North Atlantic Ocean and sea ice modeling and data assimilation

Posted on:2009-09-24Degree:Ph.DType:Dissertation
University:University of Alberta (Canada)Candidate:Rattan, Sanjay S. PFull Text:PDF
GTID:1440390005954521Subject:Physical oceanography
A number of experiments have been performed with the Subpolar Ocean Model (SPOM) and the Nucleus for European Modeling of the Ocean (NEMO) coupled ocean sea ice model to improve the models and then to utilize them for scientific process studies of the North Atlantic ocean and sea ice.In order to reduce the problem of model drift, we implement variable eddy transfer coefficient in the Gent and McWilliams eddy parameterization, and a recent semi-diagnostic assimilation method (SDV) in the SPOM model. The combined approach reduces the drift in freshwater content of the Labrador Sea almost completely, while simultaneously improving its circulation. Previous eddy-permitting modeling studies in the sub-polar North Atlantic have failed to provide accurate representation of circulations and freshwater content simultaneously. The SDV approach also represents the total and eddy heat and freshwater transports equally well.The SDV approach is also implemented in the NATL4 configuration of the NEMO model. The configuration reproduces realistic large-scale spatial and seasonal variations of sea ice in terms of concentration, thickness and extent, in agreement with observations. NATL4 has also captured important ice features along Eastern Canadian and Greenland coasts, a deficiency observed in the few previous coupled ocean-sea ice modeling studies in this region. Two sensitivity studies performed show that the sea ice in the model is sensitive to both oceanic eddy parameterization and oceanic data assimilation, with sensitivity to former being larger.An important issue facing eddy-permitting models of the North Atlantic is salinity drift of the Labrador Sea. There are a number of causes for this problem mainly arising from misrepresentations of the export of sea-ice from the Arctic Ocean, river runoff, meltwater from the Greenland ice cap and salt transport originating from the eastern subpolar gyre. In this study we investigate the salt transport originating from the eastern subpolar gyre, using two solutions of the NEMO model with different water formations. Analysis shows a gradual progression of Subpolar Mode Water (SMPW) properties from the eastern subpolar gyre to the Labrador Sea through Cape Farewell, implying the eastern subpolar gyre as an important source of the salt for Labrador Sea.
Keywords/Search Tags:Sea, Model, Ocean, Eastern subpolar gyre, North atlantic
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