Abstract
In order to solve the so-called “bull-eye” problem caused by using a simple bilinear interpolation as an observational mapping operator in the cost function in the multigrid three-dimensional variational (3DVAR) data assimilation scheme, a smoothing term, equivalent to a penalty term, is introduced into the cost function to serve as a means of troubleshooting. A theoretical analysis is first performed to figure out what on earth results in the issue of “bull-eye”, and then the meaning of such smoothing term is elucidated and the uniqueness of solution of the multigrid 3DVAR with the smoothing term added is discussed through the theoretical deduction for one-dimensional (1D) case, and two idealized data assimilation experiments (one- and two-dimensional (2D) cases). By exploring the relationship between the smoothing term and the recursive filter theoretically and practically, it is revealed why satisfied analysis results can be achieved by using such proposed solution for the issue of the multigrid 3DVAR.
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Foundation item: The National Basic Research Program of China under contract No. 2013CB430304; the National High-Tech R&D Program of China under contract No. 2013AA09A505; the National Natural Science Foundation of China under contract Nos 41030854, 40906015, 40906016, 41106005 and 41176003.
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Li, W., Xie, Y. & Han, G. A theoretical study of the multigrid three-dimensional variational data assimilation scheme using a simple bilinear interpolation algorithm. Acta Oceanol. Sin. 32, 80–87 (2013). https://doi.org/10.1007/s13131-013-0292-6
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DOI: https://doi.org/10.1007/s13131-013-0292-6