Application of the Gaussian anamorphosis to assimilation in a 3-D coupled physical-ecosystemmodel of the North Atlantic with the EnKF: a twin experiment

[摘要] We consider the application of the Ensemble Kalman Filter (EnKF) to a coupledocean ecosystem model (HYCOM-NORWECOM). Such models, especially the ecosystemmodels, are characterized by strongly non-linear interactions active in oceanblooms and present important difficulties for the use of data assimilationmethods based on linear statistical analysis. Besides the non-linearity ofthe model, one is confronted with the model constraints, the analysis statehaving to be consistent with the model, especially with respect to theconstraints that some of the variables have to be positive. Furthermore thenon-Gaussian distributions of the biogeochemical variables break an importantassumption of the linear analysis, leading to a loss of optimality of thefilter. We present an extension of the EnKF dealing with these difficultiesby introducing a non-linear change of variables (anamorphosis function) inorder to execute the analysis step in a Gaussian space, namely a space wherethe distributions of the transformed variables are Gaussian. We present alsothe initial results of the application of this non-Gaussian extension of theEnKF to the assimilation of simulated chlorophyll surface concentration datain a North Atlantic configuration of the HYCOM-NORWECOM coupled model.

[学科分类] 海洋学与技术