CoAuthors

Mikitoshi Hirabara (Japan Meteorological Agency, Japan); Takuma Yoshida (Japan Meteorological Agency, Japan)

The Japan Meteorological Agency (JMA) had been operating the Western North Pacific Ocean Data Assimilation System (MOVE/MRI.COM-WNP: hereafter referred to as the "old system") since March 2008 in order to monitor and forecast ocean conditions in the North Pacific Ocean and the seas around Japan. The old system consisted of the Western North Pacific Model (WNP: horizontal resolution of about 10 km) and the North Pacific Model (NP: horizontal resolution of about 50 km), and used the three-dimensional variational method (3DVAR) for data assimilation. The old system was capable of resolving medium-scale eddies in the seas around Japan and major ocean currents such as the Kuroshio Current, but its horizontal resolution was too coarse to represent coastal bathymetry, and it did not include tidal processes or the effects of sea-level rise and fall due to atmospheric pressure, making it difficult to represent coastal sea state changes (rapid sea-level rise, abnormal tide).
Therefore, the JMA has newly developed MOVE/MRI.COM-JPN (MOVE-JPN), which covers the seas around Japan with a horizontal resolution of 2 km, as a system capable of monitoring and forecasting such coastal phenomena, and started its actual operation in October 2020. MOVE-JPN consists of an analysis system that assimilates ocean observation data and simulates the latest ocean state, and a prediction system that initializes higher-resolution models using pre-computed analysis and forecasts the future ocean state as boundary conditions. The analysis system consists of a global three-dimensional variational system (G3-3DVAR) and a North Pacific four-dimensional variational system (NPR-4DVAR). Boundary conditions of the NPR model are given by the global analysis model through 1-way offline nesting. The prediction system is composed of GLB, NP, and JPN models and is initialized by the incremental analysis updates (IAU) scheme. The JPN model is 1-way nested to the 2-way nested set of the GLB and NP models, all of which explicitly represent tidal motion. The new system is expected to contribute to ocean state information put on the JMA web site, and to be used to support maritime traffic, fisheries, oil spills, and other activities such as searching for ships and aircraft in distress.
JMA has a plan to introduce Sentinel-3A/B and HY-2B altimeter sea level anomaly (SLA) data to MOVE–JPN, which is now using Jason-3, SARAL and Cryosat-2 along-track SLA data from CMEMS. SLA is assimilated after exclusion of two nonsteric components, namely the global ocean mass change and the sea level variations due to the barotropic response to atmospheric forcing. In the presentation, we will show the results of the impact of assimilating additional SLA data(Sentinel-3A/B, HY-2B).