[A-CG32] 中緯度大気海洋相互作用

[ACG32-P15] One-year lead predictability of oceanic variability off the eastern coast of Japan

*田村 優樹人^1,2、木戸 晶一郎²、野中 正見² (1.東京大学大学院理学系研究科地球惑星科学専攻、2.海洋研究開発機構 アプリケーションラボ)

キーワード：海洋熱波、アンサンブル予測、中規模渦、黒潮続流、渦解像海洋モデル

The frequency of marine heatwaves off the eastern coast of Japan has risen since the 2010s, with huge impacts on marine ecosystems, atmosphere aloft and even human society. Previous study has suggested an anticyclonic eddy shed from the Kuroshio Extension is a primary driver of these anomalous events. Due to strong mesoscale eddy activity associated with intense baroclinicity, predictability of oceanic variability over the region with non-eddy resolving ocean models is quite limited. Indeed, the predictable timescales of such events with existing dynamical prediction systems are limited to a few months. This study investigates predictability of seasonal to interannual oceanic variability in such an eddy-energetic region using an eddy-resolving ensemble forecasting system called JCOPE-FGO, which is based on an ocean general circulation model (OGCM) with 0.1º horizontal resolutions and data assimilation with a 3DVAR scheme (Kido et al. 2023, Geophys. Res. Lett.). Here, we have initialized the OGCM from the assimilated ocean state on January 1st of each year from 1994 to 2020, and integrated forward in time up to 3 years with two types of atmospheric forcing: interannually varying and climatological fields. Somewhat surprisingly, moderate forecast skills in surface and sub-surface temperature are found at 1-year or longer lead time to the south of Hokkaido even with the climatological forcing forecast experiment. Further analyses suggest the source of the predictability comes from an anticyclonic eddy detached from the Kuroshio Extension and its northward propagation to the high-skill region. Such phenomenon is found in both the observation and the prediction experiments, particularly during one of the prominent warming events in 2015/16.