Fast data assimilation using a nonlinear Kalman filter and a model surrogate: An application to the Columbia River estuary |
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| Institution: | 1. College of Physics and Information Engineering, Fuzhou University, Fuzhou 350108, Fujian, P. R. China;2. Faculty of Engineering and Information Technology, University of Technology Sydney, Sydney, NSW 2007, Australia;3. Commonwealth Scientific and Industrial Research Organisation, Sydney, NSW 2122, Australia;4. Division of Engineering in Medicine, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Cambridge, MA 02139, USA;5. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA;6. Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts 02115, USA;7. College of Environment and Resources, Fuzhou University, Fuzhou 350108, Fujian, P. R. China |
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| Abstract: | A fast and adjoint-free nonlinear data assimilation (DA) system was developed to simulate 3D baroclinic circulation in estuaries, leveraging two recently developed technologies: (1) a nonlinear model surrogate that executes forward simulation three orders of magnitude faster than a forward numerical circulation code and (2) a nonlinear extension to the reduced-dimension Kalman filter that estimates the state of the model surrogate. The noise sources in the Kalman filter were calibrated using empirical cross-validation and accounted for errors in model and model forcing.The DA system was applied to assimilate in situ measurements of water levels, salinities, and temperatures in simulations of the Columbia River estuary. To validate the DA results, we used a combination of cross-validation studies, process-oriented studies, and tests of statistical and dynamical consistency. The validation studies showed that DA improved the representation of several important processes in the estuary, including nonlinear tidal propagation, salinity intrusion, estuarine residual circulation, heat balance, and response of the estuary to coastal winds. |
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