Study on Observing System Simulation Experiments (OSSE) for Ocean Forecasting Based on Observation Networks of Korea

This study evaluates the effectiveness of simulation accuracy based on the Korean Ocean Research Stations (KORS), and it suggests the optimal design of ocean observation networks using Observing System Simulation Experiments (OSSE) focused on the South Sea of Korea. The virtual observation points used in the OSSE were set based on the locations of operational mooring buoys managed by the Korea Hydrographic and Oceanographic Agency (KHOA), the Korea Meteorological Administration (KMA), and KORS. The numerical model of the study area was established to consider the Exclusive Economic Zone (EEZ) around the South Sea of Korea. Also, an unstructured grid ocean model was applied considering the irregular topographical characteristics of the South Sea. This simulation experiment used meteorological and external forcing from the Korea Operational Oceanographic System (KOOS), which is operated by the Korea Institute of Ocean Science and Technology (KIOST). The 'true state' for OSSE was assumed to be the Coastal KOOS, and data assimilation was applied to preset observation points and groups. A total of 38 OSSE experiments were conducted for the summer of 2022. Results indicate that buoys located south of Jeju Island significantly improved surface current velocity, temperature, and salinity simulations along the South Sea coast. However, the accuracy of the sea surface temperature (SST) was improved only when the differences between existing observations and the background state exceeded a critical value. By applying this, considering the bias of observation buoys in forecasting systems using satellite data can improve prediction accuracy. Improvements were observed in current and salinity about seasonal variability, but the effects on short-term variability, which is less in scale, were less pronounced than SST. Future studies aim to extend the OSSE study to underscore the importance of observation network design based on Sea of Korea and improve the prediction accuracy of corresponding real-time ocean forecasting systems.