AN OCEAN DATA ASSIMILATION SYSTEM FOR CLIMATE MONITORING

An ocean data assimilation system developed for climate monitoring at the Japan Meteorological Agency (JMA) is described. The system consist s of an ocean general circulation model (OGCM) and a subsurface temper ature analysis scheme using optimal interpolation. The analyzed temper atures are continuously assimilated into the wind-driven OGCM. The atm ospheric forcing is obtained from the operational numerical weather pr ediction system. The dynamical ocean model helps synthesize informatio n in the forcing and data, neither of which is complete for analyzing subsurface structures. The temporary and spatially continuous estimate s given by the system aid the operational long-range forecasters to mo nitor climatically important phenomena such as EI Nino-Southern Oscill ation more closely on intraseasonal to interannual time scales. The in troduction of temperature data significantly improves the quality of t he wind-forced simulation of subsurface thermal fields. However, the m odel's inability to reproduce the Equatorial Undercurrent with suffici ent strength appears to limit the impact of data on the current field. Improvements in the model and in the data assimilation scheme and int roduction of other types of observational data are required for furthe r development of the system.