Ocean data assimilation: a case for ensemble optimal interpolation

The Bluelink forecast and reanalysis system is comprised of a high resolution ocean general circulation model and an ensemble optimal interpolation (EnOI) system. The Bluelink system has been integrated for a series of 15-year reanalyses and is run operationally at the Bureau of Meteorology to produce short-range ocean forecasts. This system has performed robustly, demonstrating reliable skill that is comparable to other ocean forecast systems around the world. One of the key components of Bluelink is the EnOI system. This system has proved to be a valuable and flexible tool for both operational and research applications. Drawing on Bluelink outcomes and a series of experiments with simple models, a case for using EnOI for ocean data assimilation is made. This includes a discussion of the benefits of EnOI as well as its known limitations. EnOI is robust, flexible, portable and inexpensive, and is not burdened with the technical difficulties that some other methods carry. EnOI is readily applied for coupled data assimilation and may be an appropriate choice for coupled forecast systems.