Abstract
Abstract. Assimilation of high-frequency (HF) radar current observations and CTD hydrography is performed with the 4D-Var analysis scheme implemented in the Regional Ocean Modeling System (ROMS). We consider both an idealized case, with a baroclinic slope current in a periodic channel, and a realistic case for the coast of Vesterålen in northern Norway. In the realistic case, the results of the data assimilation are compared with independent data from acoustic profilers and surface drifters. Best results are obtained when background error correlation scales are small (10 km or less) and when the data assimilation window is short, i.e. about 1 day. Furthermore, we find that the impact of assimilating HF radar currents is generally larger than the impact of CTD hydrography. However, combining the HF radar currents with a few hydrographic profiles gives significantly better results, which demonstrates the importance of complementing surface observations with observations of the vertical structure of the ocean.
Highlights
Skillful ocean forecasts are of key importance for many operations at sea, especially for emergency response services such as search-and-rescue and oil spill mitigation
The aim of this study is to investigate whether assimilation of current observations from a rapidly deployable HF radar system (Kjelaas and Whelan, 2011) in a high-resolution ocean model is a feasible way to improve the regional ocean forecast during, e.g. an oil spill event
We evaluate a 3-day period using sequential data assimilation when the assimilation window is shorter than 72 h
Summary
Skillful ocean forecasts are of key importance for many operations at sea, especially for emergency response services such as search-and-rescue and oil spill mitigation. Near-surface currents are an important input to operational drift forecast models. New satellite observations include surface salinity and currents, but the uncertainty of these products still remains too high for use in models with high horizontal resolution, i.e. on the order of 1 km. Through efforts such as the International Argo Program (Roemmich et al, 2009), observations of the subsurface ocean are increasing in number, but still remain too few to resolve the vertical and horizontal density structure of, e.g. oceanic fronts
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