The implicit equal-weights variational particle smoother (IEWVPS) is a combination of the particle filter (PF) and weak-constraint 4-dimensional variational (4D-Var) method, that inherits the merits of both. The IEWVPS avoids the filter degeneracy of particle filters through an implicit equal-weights scheme and reduces the root mean square deviations (RMSDs) by introducing the 4D-Var method. This method has been tested using the Lorenz 96 model in a previous study, and we now implement it in the Regional Ocean Model System (ROMS), which is a realistic and complex ocean model. Two key problems, the representation of the analysis error covariance and the choice of the parameter $\alpha$, were solved during this implementation. With an eddy-permitting model, satellite-based sea surface height (SSH) and sea surface temperature (SST) observations were assimilated with a set of 40 particles IEWVPS scheme. Compared with the ensemble 4D-Var method, the IEWVPS can reduce the bias introduced by perturbed atmospheric forcing, effectively improving temperature simulations in the upper 50 m while maintaining the RMSD of SSH at the same level. Therefore, the cooling effect caused by typhoons in the upper ocean is better characterized under the IEWVPS scheme than with previously used method. The ratio of RMSD to the ensemble spread indicates that the ensemble quality of the IEWVPS is much better than that of the ensemble 4D-Var. In addition, the computational cost of the IEWVPS is only slightly larger than that of the ensemble 4D-Var. One additional tangent linear model integration, one additional nonlinear model integration, and perturbation fields inputs/outputs are still needed.

隐式等权变分粒子平滑器 (IEWVPS) 是粒子滤波器 (PF) 和弱约束 4 维变分 (4D-Var) 方法的组合，继承了两者的优点。IEWVPS 通过隐式等权重方案避免粒子滤波器的滤波器退化，并通过引入 4D-Var 方法降低均方根偏差 (RMSD)。该方法已在之前的研究中使用 Lorenz 96 模型进行了测试，我们现在在区域海洋模型系统 (ROMS) 中实施它，这是一个现实且复杂的海洋模型。两个关键问题，分析误差协方差的表示和参数的选择$\alpha$，在这个实现过程中得到了解决。使用涡流允许模型，基于卫星的海面高度 (SSH) 和海面温度 (SST) 观测与一组 40 个粒子的 IEWVPS 方案同化。与集合 4D-Var 方法相比，IEWVPS 可以减少扰动大气强迫引入的偏差，有效改善上层 50 m 的温度模拟，同时保持 SSH 的 RMSD 在同一水平。因此，与以前使用的方法相比，IEWVPS 方案能更好地表征上层海洋台风造成的冷却效应。RMSD 与 ensemble spread 的比率表明 IEWVPS 的集成质量比 ensemble 4D-Var 的质量要好得多。此外，IEWVPS 的计算成本仅略大于集成 4D-Var 的计算成本。