The use of a flow field correction technique for alleviating the North Atlantic cold bias with application to the Kiel Climate Model

• Published in: Ocean Dynamics
• Main Authors: Annika Drews, Richard J. Greatbatch, Hui Ding, Mojib Latif, Wonsun Park
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Zenodo 2015
• Subjects: North Atlantic cold bias Northwest corner Empirical correction techniques North Atlantic Current; north atlantic current; North Atlantic
• Online Access: https://doi.org/10.1007/s10236-015-0853-7

The North Atlantic cold bias, associated with the misplacement of the North Atlantic Current (NAC) and typically extending from the surface to 1000 m depth, is a common problem in coupled models that compromises model fidelity. We investigate the use of a flow field correction (FFC) to adjust the path of the NAC and alleviate the cold bias. The FFC consists of three steps. First, climatological potential temperature ( T ) and salinity ( S ) fields for use with the model are produced using a three-dimensional restoring technique. Second, these T , S fields are used to modify the momentum equations of the ocean model. In the third stage, the correction term is diagnosed to construct a flow-independent correction. Results using the Kiel Climate Model show that the FFC allows the establishment of a northwest corner, substantially alleviating the subsurface cold bias. A cold bias remains at the surface but can be eliminated by additionally correcting the surface freshwater flux, without adjusting the surface heat flux seen by the ocean model. A model version in which only the surface fluxes of heat and freshwater are corrected continues to exhibit the incorrect path of the NAC and a strong subsurface bias. We also show that the bias in the atmospheric circulation is reduced in some corrected model versions. The FFC can be regarded as a way to correct for model error, e.g. associated with the deep water mass pathways and their impact on the large-scale ocean circulation, and unresolved processes such as eddy momentum flux convergence. Ocean Dynamics is a green OA journal, free access in 12 months after the date of publication. Post-print available.