This work presents simulations of ocean circulation in the southwestern South Atlantic Ocean with emphasis on the São Paulo Plateau region, a unique physiographic feature at the foot of the continental slope offshore southeast Brazil, where the flow is dominated by ocean eddies and dipoles. Surface dynamics south of 23°S presents a heterogeneous circulation pattern intimately related to the presence of mesoscale features, such as meanders of the Brazil Current along the continental slope, and eddies that interacts with deep ocean features. The reproduction of these eddies at the correct time and spatial structure are quite challenging in the context of a non-assimilative model, considering the limitations imposed by the model’s numerical schemes, physical parameterizations, boundary conditions and surface forcing. In this sense, the Regional Ocean Modeling System (ROMS) 4-dimensional Variational Data Assimilation (4D-Var) module was used to increase model skill and minimize deviations from oceanic observations. Weekly observations of Sea Surface Height (SSH), daily Sea Surface Temperature (SST) fields and in situ vertical profiles of temperature and salinity from multiple sources were used in consecutive assimilation cycles to produce an accurate representation of ocean features and their variability. Both the assimilative and free run were evaluated against observations, including in situ current measurements. Results showed significant improvements of the assimilation procedure on both assimilated and non-assimilated variables, with RMSE reductions of 27% and 47% for SST and SSH, respectively, and 51% for current speed measurements during a dipole event in the São Paulo Plateau. The assimilative run was able to reproduce a remarkable event of mesoscale eddies interaction (dipole) and consequent current intensification, leading to important improvements on model skill. The correct use of observational information of open ocean surface features through data assimilation is a key factor for a proper simulation of such eddy dipole events.

这项工作展示了南大西洋西南部海洋环流的模拟，重点是圣保罗高原地区，这是巴西东南部近海大陆坡脚下的独特地貌特征，其中的流动以海洋涡旋和偶极子为主。23°S 以南的表面动力学呈现出与中尺度特征密切相关的异质环流模式，例如沿大陆坡的巴西洋流蜿蜒曲折，以及与深海特征相互作用的涡流。考虑到模型的数值方案、物理参数化、边界条件和表面强迫所施加的限制，在非同化模型的背景下，在正确的时间和空间结构上再现这些涡流是相当具有挑战性的。在这个意义上，区域海洋建模系统 (ROMS) 4 维变分数据同化 (4D-Var) 模块用于提高模型技能并最大限度地减少与海洋观测的偏差。每周观测海面高度 (SSH)、每日海面温度 (SST) 场和在连续的同化循环中使用了来自多个来源的温度和盐度的原位垂直剖面，以准确表示海洋特征及其变化​​。同化和自由运行都根据观察进行评估，包括原位电流测量。结果表明，同化和非同化变量的同化程序都有显着改进，SST 和 SSH 的均方根误差分别降低 27% 和 47%，圣保罗高原偶极子事件期间的当前速度测量值降低 51%。同化运行能够重现中尺度涡流相互作用（偶极子）和随之而来的电流增强的显着事件，从而导致模型技能的重要改进。通过数据同化正确使用开阔海面特征的观测信息是正确模拟此类涡流偶极子事件的关键因素。