An evaluation of high-resolution ocean reanalyses in the California current system Progress in Oceanography

Sparse and inconsistent coverage of ocean observations makes analysis of climate impacts on ocean physics and marine ecosystems challenging. As a result, ocean reanalyses (i.e., ocean models constrained by observations through data assimilation) were developed to provide historical ocean state estimates that are spatially and temporally uniform. Recent advances in high performance computing and the number and quality of observations have led to the development of high-resolution ocean reanalyses, which offer an opportunity to investigate coastal ocean variability with enhanced fidelity. In this study, we evaluate the ability of three high-resolution ocean reanalyses, including the Global Ocean Reanalysis and Simulations (GLORYS), the Ocean Reanalysis System version 5 (ORAS5), and the California Current System Reanalysis (CCSRA), to accurately represent ocean temperature and salinity (from the surface to the bottom), sea surface height, and mesoscale activity in the California Current Large Marine Ecosystem (CCLME). Specifically, we compare these reanalyses to a variety of assimilated and independent in situ and satellite derived observations along the U.S. west coast. We find that the reanalyses generally reproduce large-scale variability in temperature and sea surface height within the CCLME, including effects of major ENSO events and recent marine heatwaves. We also show that GLORYS and CCSRA, with their finer horizontal resolution, have enhanced fidelity in simulating nearshore ocean parameters such as coastal sea level and bottom temperature along the continental shelf. Our results suggest that these tools can be used to study the fine-scale features of the California Current System over the past several decades.

海洋观测数据覆盖稀疏且不一致，使得气候对海洋物理过程与海洋生态系统影响的分析工作颇具挑战。为此，科研人员开发了海洋再分析 (ocean reanalyses) 产品——即通过数据同化 (data assimilation) 将观测数据约束于海洋模型之中，以提供空间与时间上均一的历史海洋状态估算结果。近年来，高性能计算技术的进步、观测数据的数量与质量双提升，推动了高分辨率海洋再分析产品的研发，这类产品为以更高保真度探究近岸海洋变异性提供了契机。本研究针对三款高分辨率海洋再分析产品展开评估，包括全球海洋再分析与模拟（Global Ocean Reanalysis and Simulations，GLORYS）、海洋再分析系统第5版（Ocean Reanalysis System version 5，ORAS5）以及加利福尼亚流系再分析（California Current System Reanalysis，CCSRA），以检验它们能否准确再现加利福尼亚流大型海洋生态系统（California Current Large Marine Ecosystem，CCLME）内的海洋温盐（从表层至底层）、海表高度与中尺度活动特征。具体而言，本研究将上述再分析产品与美国西海岸沿岸的多套同化及独立原位观测、卫星衍生观测数据进行对比。研究结果表明，上述再分析产品大体上能够再现CCLME内温度与海表高度的大尺度变异性，包括主要厄尔尼诺-南方涛动（El Niño-Southern Oscillation，ENSO）事件以及近期海洋热浪的影响。本研究同时发现，GLORYS与CCSRA凭借更高的水平分辨率，在模拟近岸海洋参数（如大陆架沿岸的海平面与底层水温）方面具备更优的保真度。本研究结果显示，上述三款工具可用于探究近几十年来加利福尼亚流系的精细尺度特征。