Decadal Modulation of El Niño Southern Oscillation and Its Interactions with Tropical Pacific Climate

厄尔尼诺Niño-Southern涛动（ENSO）的性质经历了年代际变化，但这些变化的原因尚不清楚。本研究探讨了极端ENSO事件的自调节机制，表明极端ENSO事件应该在十年时间尺度上发生。其机制取决于ENSO活动与热带太平洋平均状态之间的双向相互作用，其中El Niño和La Niña之间的空间不对称是ENSO弱态和强态转换的原因。利用耦合环流模式（CGCM）、中间耦合模式和仅海洋模式对观测资料和数值试验进行分析，探讨这一机制，了解ENSO的年代际变率及其与热带太平洋气候的相互作用。调查将集中在以下几个问题上：(1)在不同类型的ENSO动力下，ENSO与太平洋气候如何相互作用？(2) El Niño和La Niña空间不对称的原因是什么？为什么在强ENSO状态和弱ENSO状态之间发生逆转？(3)印度洋和季风在ENSO年代际变化中起什么作用？假设的ENSO-Pacific气候相互作用机制是否需要修改以包括印度洋和季风的影响？(4) ENSO年代际变率、提出的机制与1976/77年的快速气候变化之间是否存在联系？这项研究将利用为政府间气候变化专门委员会第四次评估报告编制的前所未有的高质量CGCM综合资料。这些模式模拟的ENSO行为的多样性意味着它们具有不同的ENSO动力学，因此构成了一个测试平台，用于研究不同ENSO动力学和不同温室气体强迫下ENSO-太平洋气候相互作用。将使用两个cgmcm和一个中间耦合模式进行数值试验，以限制海洋-大气耦合到单个海洋盆地或限制太平洋基本状态。将利用观测数据和海洋模式模拟来验证模式结果。本研究的更广泛影响包括改进极端ENSO事件的长期预测和改进cccms中ENSO模拟的潜力。培养博士生，招收地球系统科学专业的本科生参与研究。

Properties of the El Niño-Southern Oscillation (ENSO) undergo decadal variations, but the causes of these variations are not yet understood. This study explores a self-modulation mechanism that suggests extreme ENSO events should occur on decadal timescales. The mechanism depends on a two-way interaction between ENSO activity and the mean state of the tropical Pacific, in which the spatial asymmetry between El Niño and La Niña is responsible for transitions between weak and strong ENSO states. Analyses of observational data and numerical experiments using coupled general circulation models (CGCM), an intermediate coupled model, and an ocean only model, will be carried out to examine this mechanism and to understand decadal ENSO variability and its interaction with the tropical Pacific climate.Investigations will focus on the following issues: (1) How do ENSO and Pacific climate interact under various types of ENSO dynamics?(2) What is the cause of the spatial asymmetry between El Niño and La Niña and why does it reverse between a strong ENSO state and a weak ENSO state? (3) What roles do the Indian Ocean and monsoons play in the decadal ENSO variability? Does the hypothesized ENSO-Pacific climate interaction mechanism need to be modified to include the effects of the Indian Ocean and monsoons? (4) Are there any linkages between decadal ENSO variability, the proposed mechanism, and the 1976/77 rapid climate shift? This study will make use of the unprecedented collection of high-quality CGCM integrations that were produced for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The variety of ENSO behaviors simulated by these models implies that they have different ENSO dynamics and so comprise a test bed for examining ENSO-Pacific climate interaction under different ENSO dynamics and different greenhouse gas forcings. Numerical experiments that limit ocean-atmosphere coupling to individual ocean basins or constrain the Pacific basic state will be performed with the two CGCMs and an intermediate coupled model. Model results will be verified using observational data and simulations with an ocean model.Broader impacts of this study include the potential to improve long-term predictions of extreme ENSO events and to improve the simulation of ENSO in CGCMs. Ph.D. students will be trained, and undergraduate Earth System Science majors will be involved in the research.