Variability of the California Current System Derived from 4D-Var Circulation Estimates

将使用区域海洋模拟系统（ROMS）和4维变分（4D-Var）数据同化对美国西海岸海洋环流和加利福尼亚洋流系统（CCS）进行全面分析。1981-2011年期间的海洋观测资料将与海洋表面强迫和开放边界条件的最佳现有估计一起被吸收到ROMS中。本研究项目的目标是：(1)对近30年来的海洋环流进行回顾性分析；(2)利用分析记录和了解春夏分层的变化，以及这些变化与风应力和风应力旋度的变化如何影响上升流强度和上升流源水深；(3)在季内-年际和年代际时间尺度上确定环流变化的主要时空模态，以及这些模态与太平洋年代际涛动和北太平洋环流涛动等气候模态的关系；(4)量化对现场观测网和卫星观测网分析的影响；(5)通过数据服务器向整个社会提供循环分析，以供科学和海洋资源管理应用。这项研究将首次对加利福尼亚洋流系统环流进行分析，该环流是由区域大气模式提供的最佳海洋表面通量所强迫的区域海洋模式产生的。此外，这种同化海洋模式的独特之处在于，它提供了对分析中预期误差的正式估计，并提供了对每次观测对由此产生的环流估计的任何方面的影响的定量评估。分析误差估计对于建立分析的可信度至关重要，观测影响和观测灵敏度研究可以在未来用于设计最佳观测阵列。所提出的分析的副产品是地表强迫场和开放边界条件修正，这些修正提供了关于这些场和模式中的潜在误差的信息。研究人员是一支经验丰富的海洋建模团队，他们在CCS和4D-Var数据同化建模方面都有丰富的经验，首席研究员是ROMS 4D-Var系统的主要开发人员之一。所提出的回顾性海洋分析之所以重要，有以下几个原因：(i)它们可用于量化周至年代际尺度的变率，以及主要环流特征的趋势，特别是在观测不充分的地下区域；它们在模式的全网格上以高时间分辨率完全实现环流，基本上不存在经常困扰观测的采样和混叠问题；（三）它们可用于检验关于海洋动力学、气候变率和气候变化的假设。由此产生的分析将以数据档案的形式形成一个有价值的社区资源，可用于许多应用，包括：CCS的过程研究；驱动线下生态系统和基于个人的模型的输入；为嵌套在本地ROMS CCS网格中的高分辨率模型提供开放边界条件；以及发展海洋预报系统的初始条件，仅举几例。该项目还将为一名研究生和博士后研究人员提供先进的4D-Var数据同化方法的培训，因为我们继续培训下一代海洋数据同化者非常重要。拟议的研究还将使用4D-Var的伴随物，这是这项工作的原创和变革方面。该项目还将补充美国国家科学基金会海洋观测计划，并将支持美国西海岸综合海洋观测系统内的综合活动、用户产品开发和阵列评估。

A comprehensive analysis of the U.S. west coast ocean circulation and California Current System (CCS) will be performed using the Regional Ocean Modeling System (ROMS) and 4-Dimensional Variational (4D-Var) data assimilation. Ocean observations from the period 1981-2011 will be assimilated into ROMS, in conjunction with the best available estimates of ocean surface forcing and open boundary conditions. The goals of this research project are: (1) To perform retrospective analyses of the ocean circulation during the last 3 decades; (2) Use the analyses to document and understand changes in spring-summer stratification and how these changes, along with variations in wind-stress and wind-stress curl, influence upwelling intensity and upwelling source water depth; (3) Identify the dominant space-time modes of circulation variability on intraseasonal-to-interannual and decadal timescales and how these modes are related to climate modes such as the Pacific decadal Oscillation and North Pacific Gyre Oscillation; (4) Quantify the impact on the analyses of the in situ and satellite observing networks; (5) Make the circulation analyses available via a data server to the community at large for scientific and marine resource management applications.Intellectual meritThis research will yield the first analyses of the California Current System circulation generated by a regional ocean model forced by the best available ocean surface fluxes from regional atmospheric models. Also, this assimilative ocean model is unique in that it provides formal estimates of the expected error in the analyses, and provides a quantitative assessment of the impact of each individual observation on any aspect of the resulting circulation estimates. Analysis error estimates are critically important for establishing confidence in the analyses, and observation impact and observation sensitivity studies can be used in the future to design optimal observing arrays. A by-product of the proposed analyses are fields of surface forcing and open boundary condition corrections that provide information about potential errors in these fields and errors in the model. The investigators are a uniquely qualified and experienced team of ocean modelers, all with considerable experience in both modeling the CCS and 4D-Var data assimilation, and the lead investigator is one of the lead developers of the ROMS 4D-Var system.Broader impactsThe proposed retrospective ocean analyses are significant for a number of reasons: (i) They can be used to quantify variability on weekly to decadal timescales, and trends in the dominant circulation features, particularly in subsurface regions that are not well observed; (ii) They provide complete realizations of the circulation at high temporal resolution on the full grid of the model that are largely free of the sampling and aliasing issues that often plague observations; (iii) They can be used to test hypotheses about ocean dynamics, climate variability, and climate change. The resulting analyses will form a valuable community resource in the form of a data archive that can be used for numerous applications, including: process studies of the CCS; input for driving offline ecosystem and individual based models; a source of open boundary conditions for higher resolution models nested within the native ROMS CCS grid; and initial conditions for the development of ocean hindcasting/forecasting systems, to name but a few. This project will also provide training for a graduate student and post-doctoral researchers in advanced 4D-Var data assimilation methods, since it is important that we continue to train the next generation of ocean data assimilators. The proposed research will also use the adjoint of 4D-Var which is an original and transformative aspect of this work. This project will also complement the NSF Ocean Observatories Initiative, and will support synthesis activities, development of user products, and array assessment within the U.S. Integrated Ocean Observing Systems along the U.S. west coast.