Application of WRF Dynamical Downscaling of JRA-3Q to Wave Simulation in Inner-Bay Area

Well-developed long-term climate reanalysis data are immensely useful in ocean wave prediction systems and related fields such as extreme wave analysis, seasonal forecasts, and numerical model validations. The Japan Meteorological Agency (JMA) has released a new long-term reanalysis Grid Point Value (GPV) data, JRA-3Q, starting in 2022. The reanalysis covers the period from September 1947 onward and it is an improvement from their previous reanalysis JRA-55, with a more sophisticated analysis system. This is expected to improve the accuracy of the hindcast for meteorological and oceanographic data. However, if GPV data are to be employed as it is in wave estimation, the horizontal grid size of 40 km will lead to results with lower accuracy. In inner bays surrounded by land, such as Tokyo Bay, ocean winds are strongly influenced by the surrounding topography, and therefore, ocean winds that take the influence of land surface topography into account are required. To solve this problem, this study attempts to estimate ocean winds with high accuracy in some major bay areas of Japan by conducting WRF downscaling using JRA-3Q as the primary input. Specifically, JRA-3Q downscaling is performed for the Tokyo Bay, Osaka Bay, and Ise Bay areas for recent strong typhoons and followed by wave estimation. As a comparative study, downscaling of JRA-55 and ERA5, and wave estimation are performed.