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MICOM Sensitivity to Eddy-induced Mixing
Detelina Ivanova, Mats Bentsen, Mehmet Ilicak
Nansen Environmental and Remote Sensing Center
(Abstract received 04/30/2015 for session X)
ABSTRACT
We explore the sensitivity of the NorESM global climate model solution to parameters in ocean eddy-induced mixing parameterization. NorESM-1 ocean component MICOM features 3-D eddy diffusivity parameterization based on Eden and Greatbatch (2008). By varying the parameters (such as maximum diffusivity, ratio of the isopycnal diffusivity to the layer thickness diffusivity) we succeeded to improve the model performance in terms of reducing the temperature and salinity biases and AMOC intensity. The most improvement we achieved when we decreased the maximum diffusivity. An alternative 2-D version of the parameterization was implemented that homogenized vertically the eddy-induced mixing and improved the biases in the entire water column. In all of the experiments though the Southern Ocean (SO) cold and fresh bias was increased indicating that rather enhanced mixing is needed there, proven in experiment where we forced 1.5 larger magnitude mixing south of 45S. To gain further understanding of the eddy-induced mixing impact we examined the water mass formation in the model. The analysis showed deficiencies in the simulated mode water formation such as lack of or formed in rather lighter density classes and with smaller rates Subtropical Mode Water (STMW), and excessive production of Subpolar Mode Water. Turning off the layer interface thickness mixing (or GM had a significant impact on these water mode properties generating STMW in the observed density range. Further model development is undergoing to improve the eddy-induced mixing implementation in NorESM-2 MICOM.
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2015 LOM Workshop, Copenhagen, Denmark June 2nd - 4th, 2015