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<p>We performed an intercomparison of three eddy-resolving ocean reanalyses—FORA-WNP30, GLORYS12V1, and BRAN2020—for the western North Pacific over the period 1993–2016. While all three products exhibit high consistency in large-scale surface mean fields due to data assimilation, notable discrepancies are found in mesoscale variability and subsurface structures, reflecting differences in model configuration and assimilation schemes. Furthermore, a vertical section analysis along 137°E reveals discernible discrepancies in the representation of subsurface water masses among the products. FORA-WNP30, employing a four-dimensional variational (4D-VAR) scheme, exhibits high spatiotemporal variability in sea surface height (SSH). However, its sea surface salinity (SSS) variability is strongly dampened by a short restoring timescale. GLORYS12V1 retains intense coastal SSS variability due to the absence of strong surface restoring. However, it exhibits lower eddy kinetic energy levels compared to the others, likely due to dissipative viscosity parameterization. BRAN2020 shows systematic differences east of Japan, including reduced SSH variability and lower temporal correlations. These are attributed to its simplified bathymetry (capped at 5000 m), which eliminates topographic steering effects and alters eddy propagation speeds. Additionally, BRAN2020 exhibits a weaker vertical salinity contrast around the North Pacific Intermediate Water (NPIW), suggesting the influence of excessive vertical mixing. Our results highlight that horizontal resolution is not the sole determinant of performance; bathymetry, subgrid-scale parameterizations, and boundary conditions play equally critical roles in reproducing regional ocean dynamics.</p>

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An intercomparison of eddy-resolving ocean reanalyses in the western North Pacific

  • 期刊论文

  • 发表日期：

    2026年6月30日

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  • Nobumasa Komori,
  • Norihiko Sugimoto,
  • Kent Kumeta,
  • Hiona Mori,
  • Yoshiaki Miyamoto,
  • Naoki Hirose

摘要

We performed an intercomparison of three eddy-resolving ocean reanalyses—FORA-WNP30, GLORYS12V1, and BRAN2020—for the western North Pacific over the period 1993–2016. While all three products exhibit high consistency in large-scale surface mean fields due to data assimilation, notable discrepancies are found in mesoscale variability and subsurface structures, reflecting differences in model configuration and assimilation schemes. Furthermore, a vertical section analysis along 137°E reveals discernible discrepancies in the representation of subsurface water masses among the products. FORA-WNP30, employing a four-dimensional variational (4D-VAR) scheme, exhibits high spatiotemporal variability in sea surface height (SSH). However, its sea surface salinity (SSS) variability is strongly dampened by a short restoring timescale. GLORYS12V1 retains intense coastal SSS variability due to the absence of strong surface restoring. However, it exhibits lower eddy kinetic energy levels compared to the others, likely due to dissipative viscosity parameterization. BRAN2020 shows systematic differences east of Japan, including reduced SSH variability and lower temporal correlations. These are attributed to its simplified bathymetry (capped at 5000 m), which eliminates topographic steering effects and alters eddy propagation speeds. Additionally, BRAN2020 exhibits a weaker vertical salinity contrast around the North Pacific Intermediate Water (NPIW), suggesting the influence of excessive vertical mixing. Our results highlight that horizontal resolution is not the sole determinant of performance; bathymetry, subgrid-scale parameterizations, and boundary conditions play equally critical roles in reproducing regional ocean dynamics.