Sea Level Variability in the East Sea and East China Sea: Insights from Observations and Reanalysis (1993-2023)

This study investigates sea level variability in the East Sea (ES) and East China Sea (ECS) using a combination of in-situ observation, satellite altimeter data from the Copernicus Marine Environment Monitoring Service (CMEMS), and reanalysis datasets from the Hybrid Coordinate Ocean Model (HYCOM), Ocean Reanalysis System 5 (ORAS5), and Global Ocean Reanalysis and Simulation (GLORYS) for the period 1993-2023. The analysis focuses on the influences of steric effects and mass components on sea level, excluding atmospheric pressure impacts for simplification. The Ieodo Ocean Research Station (IORS), located in the ECS at 125.18°E and 32.12°N, served as a key observation point. The trends in monthly mean sea level were 5.82 mm yr^-1 (in-situ, 2003–2023) and 3.53 mm yr^-1 (CMEMS, 1993–2023), 3.09 mm yr^-1 (GLORYS, 1993–2023), 2.27 mm yr^-1 (ORAS5, 1993–2023) and -0.09 mm yr^-1 (HYCOM, 1994–2023). Notably, HYCOM trends exhibited variability over sub-periods, with rates of 0.85 mm yr^-1 (1994-2015), 2.75 mm yr^-1 (2016-2023), 0.56 mm yr^-1 (1994-2017), 8.82 mm yr^-1 (2018-2023), and 0.56 mm yr^-1 (2003-2023). Cross-correlation analysis demonstrated significant agreement between detrended sea levels, with coefficients of 0.92 (CMEMS & GLORYS), 0.90 (CMEMS & HYCOM), 0.89 (CMEMS & ORAS5), 0.80 (CMEMS & in-situ). Additionally, this methodology was applied to sea level data from Ulleung Island at 130.90°E and 37.50°N and Dok Island at 131.87°E and 37.24°N, providing further insights into sea level variability in the ES and ECS. Understanding sea level changes in these regions using limited but representative datasets contributes to improving knowledge of regional sea level variability and supports analysis and prediction in a warming climate.