A univariate statistical interpolation scheme for subsurface thermal analyses in the tropical oceans

Abstract A scheme for real-time objective analysis and quality control of ocean temperature data using statistical interpolation is presented. The data base comprises BATHY and TESAC message summaries of XBT profiles collected in real-time under the ship-of-opportunity program, as well as directly recorded data which are collected and archived some time after the observation time. The subsurface temperature observations, spread irregularly in time and space and of mixed quality, are first verified against climatology and other observations before interpolation onto a regular grid. The analysis procedure is based on univariate statistical interpolation techniques which are in standard use throughout the meteorological community. Attention is focused on the elimination of bad or inconsistent measurements and unwanted redundancy. A non-trivial observation error autocorrelation function is incorporated to take account of spatial and temporal coherency of geophysical noise along XBT tracks. A novel technique for combining partial analyses from over-lapping sectors is also presented. The efficacy of the scheme is demonstrated through a series of examples based on tropical Pacific Ocean observations for the last several years. The appropriateness of the statistical models and first-guess field is evaluated and the practical implementation of super-observation formation and data checking is illustrated. An assessment of the real-time Pacific Ocean analysis system for two years, through statistics and direct map evaluation, indicates the scheme is performing well. Information is not communicated between analysis periods, a role which we expect statistical and dynamical models to assume in future.

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