Nowcasting and forecasting of ocean jets and eddies using a semi-global eddy-resolving ocean prediction system

Increasing evidence from observational and modelling studies have demonstrated that frontal-scale ocean variability, such as meandering of jets and mesoscale eddies, plays an important role in water-mass formation, air-sea interaction, and transports of active and passive tracers. While our understanding on characteristics and driving mechanisms of oceanic fronts and eddies have been significantly advanced in recent decades, an accurate monitoring and prediction of these frontal-scale ocean variability and their possible coupling with the atmosphere are still difficult even for the state-of-the-art ocean and climate models. As a first step to archive this goal, an intensive research project focusing on the mid-latitude ocean- atmosphere interaction processes (called “Climatic Hotspot2”) was initiated in Japan from 2020. As a part of this project, we have developed a novel ocean nowcasting and forecasting system (named as the JCOPE-FGO) that covers the quasi-global ocean (75°S-75°N) with a horizontal resolution of 0.1°x0.1°. By assimilating various kinds of satellite and in-situ observations into an eddy-resolving ocean general circulation model (OGCM), the JCOPE-FGO provides estimates of three-dimensional fields in the world oceans and forecasts of their evolutions at multiyear timescale. In this presentation, I will introduce overview of the JCOPE-FGO system and discuss results from a series of forecasting experiments. Specifically, I will demonstrate that our newly developed system can better capture observed frontal-scale ocean variability compared to other existing ocean reanalysis products with coarser spatial resolutions. I will also present results from forecasting experiments to demonstrate that observed year-to-year variations in the intensities of the jets and eddies in the Kuroshio Extension and Gulf Stream regions are predictable up to the lead times of about 2 years, when an eddy-resolving OGCM is initialized with the reanalysis fields of the JCOPE-FGO. Implications of our results for high-resolution coupled climate modelling will also be discussed during the seminar.