Assimilation of XBT Data Using a Variational Technique
For several years meteorologists have used different statistical techniques to combine model and observations to obtain a good analysis of the atmospheric state. One of the most successful and widely used methods in operational weather centres is optimal interpolation, denoted OI (Gandin, 1965; Lorenc, 1986; Hollingsworth, 1987), whereby one tries to minimize the mean square error between the truth state and the analysed state of the system at a given time. This is attempted by constructing an analysis which is a linear combination of a priori field plus the weighted sum of the observational deviations from this preliminary field. Operationally, a short range forecast constitutes the preliminary field. Constraints on the time evolution of the system are not imposed, since O.I. (as currently used) is an analysis at a single time.
KeywordsLagrange Multiplier Wind Stress Conjugate Gradient Algorithm Adjoint Method Thermocline Depth
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