Improved estimates of heat and water mass transports in the Pacific Ocean by a long-term data assimilation experiment using a 4-dimensional variational approach

我们研究的主要目标是构建一个创新的四维变分(4D-VAR)数据同化系统，能够提供高质量的综合数据集。通过变分方法合成观测数据和最新的大气环流模式，能够产生动态自洽的时空数据集。为了实现我们的目标，我们在一台并行计算机上成功地建立了一个4D-VAR资料同化系统，并将其应用于1980年代末S之后的一个长期再分析试验中。该试验将所有的观测资料同化到一个海洋环流模式中。所获得的再分析数据集与重要气候事件的先验知识具有良好的一致性。例如，进化…Nino3 SST的更多部分被很好地再现(其误差值减少到早期模拟的1/2左右)，这支持了我们的数据集准确地反映了该地区气候变异性的概念。此外，我们的再分析数据集显示了真实的地下水团分布，并使我们能够澄清水团的形成和运动过程。对表征西北北太平洋环流的二热和中温水通道进行了敏感性试验，考察了它对亚北极太平洋地区人为成本的敏感性。伴随变量的分布与前人对副热带黑潮延伸区和西亚极区的研究具有较好的一致性。同样，中间水可以追溯到它们的源头地区。利用我们的再分析数据集，我们估计了与太平洋翻转有关的经向热量和水团输送。仔细观察经向分布，就会发现年平均值和季节变化与以往的认识基本一致。这些结果证实了我们的4D-VAR资料同化系统是理解和预报太平洋动力状态的有力工具。较少

The main objective of our research is to construct an innovative 4-dimensional variational(4D-VAR) data assimilation system capable of providing high-quality comprehensive datasets. Synthesis of observational data and state-of-the-art general circulation models by the variational approach has the ability to produce a dynamically self-consistent space-time dataset. Such datasets are urgently required for more accurate prediction and for better estimation of the dynamical state of the Pacific Ocean associated with global warming.In order to achieve our goal, we have successfully constructed a 4D-VAR data assimilation system on a parallel computer machine, and have applied it to a long-term reanalysis experiment during the period after the late 1980's. This experiment assimilated all the observational data available into an ocean general circulation model. The obtained reanalysis dataset shows good consistency with previous knowledge of important climate events. For example, the evolution … More of Nino3 SST is well reproduced (its error value reduces to about 1/2 of that from the earlier simulations), which supports the notion that our dataset accurately represents the climate variability in this region. Further, our reanalysis dataset exhibits realistic subsurface water mass distribution and enables us to clarify the water mass formation and movement processes. An application of a sensitivity experiment to the dichothermal and mesothermal water pathways that characterize the northwest North Pacific circulation is performed in which we investigate the sensitivity to an artificial cost given in the subarctic Pacific region. The distribution of adjoint variables shows good consistency with previous studies of the subtropical Kuroshio Extension region and western subarctic region. Similarly, intermediate waters can be traced back to their source regions. Using our reanalysis data set, we estimated meridional heat and water mass transports associated with the overturn in the Pacific Ocean. A close look at the meridional distributions reveal that the annual mean and the seasonal change are by and large consistent with previous knowledge. These results confirm that our 4D-VAR data assimilation system is a powerful tool for the understanding and prediction of the dynamical state of the Pacific Ocean. Less