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Abstract:
Following successful long-term work to improve the representation of Southern Ocean near surface temperatures - and reduce biases in mixed layer depths - we begin an analysis of temperature and salinity biases in the important North Atlantic region. This region is relevant to stakeholders on a variety of time and space scales. For example, the positioning of ocean fronts provides an important boundary condition for short term forecasting, whilst the representation of deep-water formation and the Atlantic Meridional Overturning Circulation are important on decadal to centennial time scales. In addition, many of the important processes and features, such as the path of the North Atlantic Current, are relevant for multiple stakeholders and time scales.
We begin by determining the temperature and salinity biases in the near surface ocean that are consistent across ocean resolution and surface boundary condition (ocean-only or coupled). To minimise differences due to model parameter choices, we use a set of 6 simulations that are designed to be broadly consistent, at ORCA1, ORCA025, and ORCA12 resolutions in both forced and coupled configurations. We focus primarily on the two higher resolution configurations.
Initial results show a complex picture of a dipole between the central subpolar gyre (warm and salty) and Gulf Stream extension (cool and fresh) consistent with a misalignment of the North Atlantic Current in both forced and coupled configurations, although the central subpolar gyre biases are stronger in forced configurations. In addition, forced configurations show a warmer and saltier northern subpolar gyre, perhaps due to differences in the forcing or overly strong ingress of North Atlantic water. Further analysis is ongoing to determine the dependence on forcing product. Our first goal is to develop a set of specific metrics using which model improvements can be tested against these baseline simulations.
