Numerical simulation and satellite altimeter data assimilation of the Japan Sea circulation

The time-evolving state of the Japan Sea is estimated by an eddy-permitting ocean general circulation model and an assimilation of TOPEX/POSEIDON (T/P) and ERS-1/2 altimeter data using an approximate Kalman filter. The simulated sea-level variabilities are interpreted in relation to the Tsushima Warm Current, the Polar Front, and the subpolar gyre. The simulated and assimilated estimates account for about 29% and 49% of the measured sea level variance, respectively, and the difference between the two is mostly attributed to mesoscale variability corrections. The formal error covariance and separate assimilation of the satellite altimeter data reveal the higher efficacy of the ERS data in detecting the mesoscale variability compared to the T/P data. The assimilation impact lasts for a few months, reflecting the long lifetime of the subpolar gyre and the mesoscale eddies.