Application of a 3D-var data assimilation scheme to an eddy-permitting North Pacific Model based on ROMS


Takashi Setou(National Research Institute of Fisheries Science, Fisheries Research Agency, Japan.)
Hiroshi Kuroda(National Research Institute of Fisheries Science, Fisheries Research Agency, Japan.)
Kazuhiro Aoki(National Research Institute of Fisheries Science, Fisheries Research Agency, Japan.)
Manabu Shimizu(National Research Institute of Fisheries Science, Fisheries Research Agency, Japan.)
Tomowo Watanabe(National Research Institute of Fisheries Science, Fisheries Research Agency, Japan.)



A three-dimensional variational (3D-var) data assimilation scheme has been developed and applied to an eddy-permitting North Pacific model based on Regional Ocean Modeling System (ROMS). Our final goal is for studying fisheries resource/recruitment variation and managing the proper marine/fisheries environment on the basis of the reanalysis or the forecast products. The 3D-var scheme is founded on the MOVE system developed by the Japan Meteorological Research Institute (e.g. Fujii and Kamachi , 2003). This scheme is characterized by the following three steps; (1) minimizing the nonlinear cost functions by using a pre-conditioning method, (2) analyzing temperature-salinity profiles by using vertical coupled EOF modes, and (3) assimilating the data analyzed into an ocean model, namely, making reliable reanalysis data by using the Incremental Analysis Updates method. As the first step, we apply this scheme to the 1/2-degree ocean model covering the whole of the North Pacific. Satellite SSH/SSTs and in situ temperature-salinity data from GTSPP and WOD2009 are assimilated into the model. It is found that the 3D-var scheme works well and significantly improves simulated results. That is, the reanalysis data is in better agreement with some observed data than the simulation without the data assimilation. For example, eddy activities west of the date-line in the mid-latitude are well reproduced in the reanalysis data.