LETKF-based Ocean Research Analysis (LORA): A new ensemble ocean analysis dataset

Abstract

Various ocean analysis products have been produced and used for geoscience research. In the Pacific region, there are four high-resolution regional analysis datasets [JCOPE2M (Miyazawa et al. 2017) and FRA-ROMS II (Kuroda et al. 2017) with 3D-VAR; NPR-4DVAR (Hirose et al. 2019) with 4D-VAR; and DREAMS with a Kalman filter (Hirose et al. 2013)], but there are no EnKF-based analysis datasets to the best of the authors’ knowledge. Recently geostationary satellites such as Himawari-8 and -9 have been providing sea surface temperatures (SSTs) at high spatiotemporal resolution. To use these data effectively, we have developed an eddy-permitting EnKF-based ocean data assimilation system at horizontal resolution of 0.25° with a short assimilation interval of 1 day and demonstrated that the combination of three schemes [incremental analysis update (IAU; Bloom et al. 1996), relaxation-to-prior perturbation (RTPP; Zhang et al. 2004), and adaptive observation error inflation (AOEI; Minamide and Zhang 2017)] significantly improved dynamical balance and analysis accuracy (Ohishi et al. 2022a, b). With the recent enhancement of computational resources, we have developed higher-resolution eddy-resolving ocean data assimilation systems at horizontal resolution of 0.1° and produced ensemble analysis products for the western North Pacific (WNP) and Maritime Continent (MC) regions called the LETKF-based Ocean Research Analysis (LORA)-WNP and -MC, respectively (Ohishi et al. 2023). The validation results show that the LORA has sufficient accuracy for geoscience research and various applications such as fisheries and marine transport. Since March 2023, the LORA-WNP and -MC have been released at JAXA-RIKEN Ocean Analysis website (https://www.eorc.jaxa.jp/ptree/LORA/index.html).