An Ocean Data Assimilation System for Climate Monitoring (gtSpecial IssueltData Assimilation in Meteology and Oceanography: Theory and Practice)

Abstract

An ocean data assimilation system developed for climate monitoring at the Japan Meteorological Agency (JMA) is described. The system consists of an ocean general circulation model (OGCM) and a subsurface temperature analysis scheme using optimal interpolation. The analyzed temperatures are continuously assimilated into the wind-driven OGCM. The atmospheric forcing is obtained from the operational numerical weather prediction system. The dynamical ocean model helps synthesize information in the forcing and data, neither of which is complete for analyzing subsurface structures. The temporary and spatially continuous estimates given by the system aid the operational long-range forecasters to monitor climatically important phenomena such as El Nino-Southern Oscillation more closely on intraseasonal to interannual time scales. The introduction of temperature data significantly improves the quality of the wind-forced simulation of subsurface thermal fields. However, the model's inability to reproduce the Equatorial Undercurrent with sufficient strength appears to limit the impact of data on the current field. Improvements in the model and in the data assimilation scheme and introduction of other types of observational data are required for further development of the system.