11:30 〜 11:45
[MGI26-09] Nowcasting and forecasting of ocean fronts and eddies with an eddy-resolving quasi-global dynamical ocean system–JCOPE-FGO–
★招待講演
キーワード：Ocean data assimilation、Frontal-scale ocean variability、Western boundary currents
Oceanic fronts and eddies, which have a horizontal scale of few tens to hundred kilometers, are ubiquitous in the global ocean. Such oceanic frontal structures play a key role in various physical processes such as water-mass formation and transport of physical and biogeochemical tracers, and exert widespread impacts on various related fields including regional and global climate as well as fisheries. While many regional dynamical ocean nowcasting and forecasting systems have been developed to understand characteristics and predictability of frontal-scale oceanic variability, the current generation of global ocean and climate prediction systems are still too coarse to resolve these frontal features. Thus, there is a large gap between our knowledge on regional- and global-scale ocean variability, and their coordinated description and prediction are highly warranted.
As a first step to achieve the above goal, our group have recently developed a semi-global eddy-resolving ocean reanalysis and forecasting system, named the Japan Coastal Ocean Predictability Experiments-Forecasting Global Ocean (JCOPE-FGO). This system is a global extension of the regional JCOPE system originally configured for the western North Pacific, and it covers the global ocean from 75°S to 75°N with a horizontal resolution of about 10 km. In this system, information obtained from in-situ temperature and salinity profiles and satellite observations of sea surface temperature and sea surface height are dynamically incorporated into an eddy-resolving ocean general circulation model with the 3DVAR scheme. The JCOPE-FGO provides estimates of three-dimensional oceanic states from January 1993 to present.
Comprehensive validations of analyzed oceanic fields of the JCOPE-FGO against various types of available observations revealed that this product can realistically reproduce spatial distributions of water mass structures and dynamical fields in most part of the global ocean, although some quantitative discrepancies are also identified over several specific regions. The temporal variations in these fields, including those of jets and eddies, are also correctly captured compared to other existing systems that do not explicitly resolve mesoscale eddies.
Furthermore, retrospective forecasting experiments using the reanalysis fields of the JCOPE-FGO as initial conditions revealed that year-to-year variations in intensities of jets and eddies in the Kuroshio and Gulf Stream regions can be skillfully predicted up to the lead time of about 2 years. Further analysis of predicted fields demonstrated that the source of predictability originates from the initial ocean memories and their slow propagation in form of oceanic baroclinic waves, while changes in local atmospheric condition also play a secondary role. These results suggest that observed multiyear variations in jets and eddies are indeed predictable if we use a properly-initialized eddy-resolving OGCM.
As a first step to achieve the above goal, our group have recently developed a semi-global eddy-resolving ocean reanalysis and forecasting system, named the Japan Coastal Ocean Predictability Experiments-Forecasting Global Ocean (JCOPE-FGO). This system is a global extension of the regional JCOPE system originally configured for the western North Pacific, and it covers the global ocean from 75°S to 75°N with a horizontal resolution of about 10 km. In this system, information obtained from in-situ temperature and salinity profiles and satellite observations of sea surface temperature and sea surface height are dynamically incorporated into an eddy-resolving ocean general circulation model with the 3DVAR scheme. The JCOPE-FGO provides estimates of three-dimensional oceanic states from January 1993 to present.
Comprehensive validations of analyzed oceanic fields of the JCOPE-FGO against various types of available observations revealed that this product can realistically reproduce spatial distributions of water mass structures and dynamical fields in most part of the global ocean, although some quantitative discrepancies are also identified over several specific regions. The temporal variations in these fields, including those of jets and eddies, are also correctly captured compared to other existing systems that do not explicitly resolve mesoscale eddies.
Furthermore, retrospective forecasting experiments using the reanalysis fields of the JCOPE-FGO as initial conditions revealed that year-to-year variations in intensities of jets and eddies in the Kuroshio and Gulf Stream regions can be skillfully predicted up to the lead time of about 2 years. Further analysis of predicted fields demonstrated that the source of predictability originates from the initial ocean memories and their slow propagation in form of oceanic baroclinic waves, while changes in local atmospheric condition also play a secondary role. These results suggest that observed multiyear variations in jets and eddies are indeed predictable if we use a properly-initialized eddy-resolving OGCM.