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

概述：气候动力学中的一个长期问题是低频气候变率在多大程度上是内在的还是被迫的。气候系统在很大的时间尺度上表现出变异性。最近的研究结果表明，涡分辨海洋模式表现出很大的年际变化，即使这种变化是在大气强迫缺席。这一结果表明，内在的海洋非线性几乎一样重要的大气强迫在维持低频海洋变率。早期的工作表明，非线性也会导致大气模型中的一些低频变化。学术价值：该项目解决了气候科学的一个重要问题-低频变率是自由的还是被迫的。 新工具的应用将为用来回答这一问题的其他方法提供有益的补充。拟议的工作建立在最近的研究的主要研究者，其中频率和频率波数域谱，谱转移，和光谱通量已诊断从涡流解决海洋环流模型在现实的域，从网格卫星高度计数据，并从理想化的两层QG湍流模拟驱动的强加斜压不稳定的平均流。与波数空间中的谱传输和通量一样，在地转湍流研究中，谱传输和通量在频率空间中量化了强迫、非线性和其他过程对能量和能量通量收支的相对贡献。在理想化的两层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。拟议的工作将把这一分析扩展到耦合气候模式的海洋和大气部分，以“独立”模式和完全耦合模式运行。更广泛的影响：该项目将有助于量化和了解低频变率，并增进对涡动分辨耦合气候模型的了解，这些模型不久将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，与领先的国家气候建模实验室（NOAA/GFDL）的科学家合作，执行现实领域的结果。理想化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。本科生将被纳入研究，因为首席研究员（PI）自2006年以来一直在做。与加纳大学的合作将有助于在严重缺乏地球科学能力的非洲大陆发展这种能力。PI和他的团队的三名成员-一名加纳血统的博士后和两名美国研究生-每年夏天将访问加纳大学海洋学系两周。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发展技能，如使用Matlab，使用卫星高度计产品，并熟悉海洋模型。该项目建立在PI对非洲科学发展的持续兴趣的基础上，这是他在加纳担任和平队志愿者教师期间产生的，并且与PI在非洲的机构的大量投资是一致的。

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.