A preliminary analysis of a newly-developed regional ocean data assimilation system: a case of Tokyo Bay in summer
This study shows preliminary results from a newly-developed regional ocean data assimilation system, ROMS-LETKF, which consists of a regional ocean model ROMS and the local ensemble transform Kalman filter (LETKF). This system was applied for Tokyo Bay at 500-m resolution with 21 ensemble members and forced by an atmospheric analysis data from the Japan Meteorological Agency Mesoscale Model (JMA-MSM). We performed a data assimilation cycle experiment for a month starting at 0000 UTC July 1, 2016 after a 1-month spin-up. We used in-situ observed temperatures and salinities at a 1-hour interval and surface currents observed by high-frequency radars at a 15-minute interval. These observation data are provided from the Tokyo Bay Environmental Information Center.
The ROMS-LETKF system works well and improves the reproducibility of the physical fields in Tokyo Bay. However, imbalance of heat between the ocean and the atmosphere causes a cold bias for ocean surface. The bias may be more evident in Tokyo Bay due to its shallow ocean floor and small exchange of water with the outer ocean. These conditions make the prescribed atmospheric forcing have a large effect. Therefore, our future research will focus on atmosphere-ocean coupled data assimilation.
Dr. Kohei Takatama RIKEN