CAREER: Diagnosis of forced versus intrinsic low-frequency variability in high-resolution coupled climate models using geostrophic turbulence techniques

概述：气候动力学中一个长期存在的问题是低频气候变率在多大程度上是内在的还是被迫的。气候系统在大范围的时间尺度上表现出变率。最近的研究结果表明，即使在大气强迫中没有这种年际变化，涡旋解析海洋模式也显示出大量的年际变化。这一结果表明，在维持低频海洋变率方面，海洋固有的非线性几乎与大气强迫同样重要。早期的研究表明，非线性也驱动了大气模式中的一些低频变率。知识价值：该项目解决了气候科学的一个重要问题——低频变化是自由的还是被迫的。新工具的应用将为用于回答这个问题的其他方法提供有益的补充。所提出的工作建立在首席研究员最近的研究基础上，在该研究中，频率和频率波数域谱、谱转移和谱通量已经从现实域的漩涡分解海洋环流模型、网格化卫星高度计数据以及由强加的临床不稳定平均流驱动的理想化双层QG湍流模拟中诊断出来。与在地转湍流研究中早已被诊断出来的波数空间的谱转移和通量一样，频率空间的谱转移和通量量化了强迫、非线性和其他过程对能量和能量通量预算的相对贡献。在理想的两层QG湍流模拟中，非线性是维持低频方差的最大项，强迫和摩擦起着重要但次要的作用。拟议的工作将把这种分析扩展到耦合气候模式的海洋和大气成分，在“独立”和完全耦合模式下运行。更广泛的影响：本项目将有助于对低频变率的量化和理解，并增加对涡旋分辨耦合气候模式的理解，这些模式将很快成为气候预测研究中广泛使用的工具。该项目为博士后科学家提供资金，与领先的国家气候模拟实验室（NOAA/GFDL）的科学家合作，进行现实领域的研究。理想的模型将由一名研究生运行和分析，该研究生已获得NSF研究生奖学金的支持。自2006年以来，首席研究员（PI）一直在做这项研究，本科生将被纳入研究。与加纳大学的合作将有助于在一个严重缺乏地球科学能力的大陆发展这种能力。每年夏天，PI和他团队的三名成员——一名加纳裔博士后和两名美国研究生——将访问加纳大学海洋系两周。在加纳大学，PI将讲授物理海洋学主题，PI的博士后和学生将帮助加纳海洋学学生培养使用Matlab、使用卫星高度计产品和熟悉海洋模型等技能。该项目建立在个人对非洲科学发展的持续兴趣的基础上，这种兴趣是他在加纳担任和平队志愿教师期间产生的，并且与个人在非洲的机构的大量投资相一致。

Overview: A long-standing question in climate dynamics is the extent to which low-frequency climate variability is intrinsic versus forced. The climate system exhibits variability over a vast range of time scales. Recent findings show that eddy-resolving ocean models exhibit substantial inter-annual variability even when such variability is absent in the atmospheric forcing. This result suggests that intrinsic oceanic nonlinearities are nearly as important as atmospheric forcing in maintaining low-frequency oceanic variability. Earlier work shows that nonlinearities also drive some of the low-frequency variability in atmospheric models. Intellectual Merit: The project addresses an important question of climate science - whether low-frequency variability is free or forced. The application of new tools will provide a useful complement to other approaches used to answer this question. The proposed work builds upon recent research by the principal investigator, in which frequency - and frequency-wavenumber domain spectra, spectral transfers, and spectral fluxes have been diagnosed from eddy-resolving ocean general circulation models in realistic domains, from gridded satellite altimeter data, and from idealized two-layer QG turbulence simulations driven by an imposed baroclinically unstable mean flow. As with spectral transfers and fluxes in wavenumber space, which have long been diagnosed in geostrophic turbulence studies, the spectral transfers and fluxes in frequency space quantify the relative contributions of forcing, nonlinearity, and other processes to the budgets of energy and energy flux. In the idealized two-layer QG turbulence simulations, nonlinearities are the largest terms in the maintenance of low-frequency variance, with forcing and friction playing important but secondary roles. The proposed work will extend this analysis to the oceanic and atmospheric components of coupled climate models, run in both "stand-alone" and fully coupled modes. Broader Impacts: This project will contribute to the quantification and understanding of low-frequency variability, and increase understanding of eddy-resolving coupled climate models, which will soon become widely used tools in climate prediction studies. The project provides funding for a postdoctoral scientist to perform the realistic-domain results, in collaboration with scientists at a leading national climate modeling lab (NOAA/GFDL). The idealized model will be run and analyzed by a graduate student, who has obtained support from an NSF graduate student fellowship. Undergraduates will be integrated into the research, as the principal investigator (PI) has been doing since 2006. Collaboration with the University of Ghana will help to develop earth science capacity in a continent where this capacity is severely lacking. The PI and three members of his group--a postdoc of Ghanaian descent, and two U.S. graduate students--will visit the oceanography department of the University of Ghana for two weeks each summer. At University of Ghana, the PI will give lectures on physical oceanographic topics, and the PI's postdoc and students will help Ghana oceanography students develop skills such as using Matlab, using satellite altimeter products, and attaining familiarity with ocean models. The project builds upon the PI's continuing interest in the development of African science, engendered during his experience as a Peace Corps volunteer teacher in Ghana, and is consistent with the substantial investment of the PI's institution in Africa.