Evaluation of near-surface potential temperature (GLORYS12V1) against in situ observations in the Viet Nam East Sea

Tóm tắt

This study evaluates the performance of the GLORYS12V1 ocean reanalysis data against in situ near-surface seawater temperature observations at eight hydrographic stations in Vietnamese coastal and offshore waters during 2003-2022. The evaluated GLORYS12V1 field is seawater potential temperature at the uppermost standard level, approximately 0.494 m depth. Monthly matched observation-reanalysis pairs were assessed using the Pearson correlation coefficient, Nash-Sutcliffe efficiency coefficient, mean absolute error, mean bias, and root-mean-square error. The analysis also examined characteristic monthly and annual mean temperature values, trends during 2003-2022, and ENSO-stratified deseasonalized anomaly errors. The results indicate that GLORYS12V1 reproduced the observed monthly temperature variability and seasonal cycle reasonably well at the eight evaluated stations, with correlation coefficients ranging from 0.869 to 0.984 and NSE values from 0.738 to 0.954. Performance varied among stations, with larger absolute errors at some Northern and North-central coastal stations and generally smaller errors at Southern and offshore stations. The regional annual mean near-surface temperature fields showed a persistent North-South thermal contrast and an increasing tendency during 2003-2022. ENSO-stratified analysis indicated differences in deseasonalized anomaly errors among La Niña, neutral, and El Niño conditions. Overall, the results provide a station-based assessment of GLORYS12V1 uppermost-level seawater potential temperature and support its use as a near-surface SST proxy at the evaluated locations, while highlighting the need for caution in coastal areas with strong seasonal and local variability.