Development, implementation and evaluation of a data-assimilative ocean forecasting system off the central California coast

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Chao, Yi
Li, Zhijin
Farrara, John
McWilliams, James C.
Bellingham, James
Capet, Xavier
Chavez, Francisco
Choi, Jei-Kook
Davis, Russ
Doyle, Jim
Data assimilation
Ocean modeling
Ocean forecast
Coastal ocean
Adaptive sampling
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The development and implementation of a real-time ocean forecast system based on the Regional Ocean Modeling System (ROMS) off the coast of central California are described. The ROMS configuration consists of three nested modeling domains with increasing spatial resolutions: the US West coastal ocean at 15-km resolution, the central California coastal ocean at 5 km, and the Monterey Bay region at 1.5 km. All three nested models have 32 vertical sigma (or terrain-following) layers and were integrated in conj. unction with a three-dimensional variational data assimilation algorithm (3DVAR) to produce snapshots of the ocean state every 6 h (the reanalysis) and 48-h forecasts once a day. This ROMS forecast system was operated in real time during the field experiment known as the Autonomous Ocean Sampling Network (AOSN-II) in August 2003. After the field experiment, a number of improvements were made to the ROMS forecast system: more data were added in the reanalysis with more careful quality control procedures, improvements were made in the data assimilation scheme, as well as model surface and side boundary conditions. The results from the ROMS reanalysis are presented here. The ROMS reanalysis is first compared with the assimilated data as a consistency check. An evaluation of the ROMS reanalysis against the independent measurements that are not assimilated into the model is then presented. This evaluation shows the mean differences in temperature and salinity between reanalysis and observations to be less than 1 degrees C and 0.2 psu (practical salinity unit), respectively, with root-mean-square (RMS) differences of less than 1.5 degrees C and 0.25 psu. Qualitative agreement is found between independent current measurements and the ROMS reanalysis. The agreement is particularly good for the vertically integrated current along the offshore glider tracks: the ROMS reanalysis can realistically reproduce the poleward California Undercurrent. Reasonably good agreement is found in the spatial patterns of the surface current as measured by high-frequency (HF) radars. Preliminary results concerning the ROMS forecast skill and predictability are also presented. Future plans to improve the ROMS forecast system with a particular focus on assimilation of HF radar current measurements are discussed.
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Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA)
Office of Naval Research (ONR) through a subcontract from MBARI to Raytheon
ONR’s program element 0601153N for J. Doyle
Computational resources for COAMPS were supported in part by the FNMOC.
Chao, Yi, et al. "Development, implementation and evaluation of a data-assimilative ocean forecasting system off the central California coast." Deep Sea Research Part II: Topical Studies in Oceanography 56.3-5 (2009): 100-126.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.