Oral

IAPSO

P05 - Regional ocean modelling

Two Skies, One Ocean: An intercomparison of regional model development and evaluation for the Maritime Continent

The Maritime Continent, with its complex system of islands and shallow seas, is influenced by several large-scale atmospheric, oceanic, and coupled climate systems, which makes weather and climate variability prediction particularly challenging for the region. To address these challenges, a high-resolution, eddy-resolving (1/12��) regional ocean model using the Nucleus for European Modelling of the Oceans (NEMO) was developed to carry out simulations across the Maritime Continent region for historical periods (1995-2014) and future projections (2015-2100). However, the reliability of such simulations is intrinsically dependent on the quality of the model��s driving data. Thus, to understand the impact of the driving data, two NEMO model configurations driven by downscaled atmospheric forcing from the ERA5-UK Met Office Unified Model (ERA5-UM) and ERA5-Weather Research Forecasting Model (ERA5-WRF) were run for the historical period. Each model configuration performance was evaluated against datasets such as CMEMS-OSTIA and ARGO. Both model configurations were able to reproduce known seasonal processes and monthly trends in temperature and salinity but exhibited varying degrees of overestimation or underestimation both at the surface and subsurface. Notably, it was found that the ERA5-UM-NEMO configuration outperformed the ERA5-WRF-NEMO configuration, by demonstrating reduced bias at the surface and within the mixed layer. To further substantially reduce model bias, our study also implemented a multi-envelope vertical coordinate system to the ERA5-UM-NEMO configuration. This enhancement accounts for improved representation of the different physical processes at different model depths and results indicated significant improvements to resolving the bias in the surface and the mixed layer. This also emphasises the critical role of the complex bathymetry within the Maritime Continent and its impact on the regional circulation. Overall, these findings provide valuable guidance for model improvement to enhance understanding of the processes underlying ocean variability across the Maritime Continent.