Collaborative Research: Testing the Indian Ocean El Nino Hypothesis

这项研究将探索印度洋是否能在持续的温室效应下维持类似厄尔尼诺的气候变化。检验这一假设很重要，因为这种模式的激活可能会导致人口稠密的印度洋边缘地区的年变化和水文极端情况发生巨大变化。这种气候变率模式在历史资料中尚未观察到，因此需要进行古气候重建，以研究有利于其出现的条件，其空间特征以及气候模型真实模拟的能力。根据气候模拟，这种模式的激活取决于印度洋的状态，印度洋目前没有表现出上升流，也没有浅温跃层（海洋水柱中温度随着深度迅速下降的区域）--这些特征需要支持海洋和大气之间强有力的大规模相互作用。古气候记录表明，这些特征可能存在于过去的地质时期，特别是在距今约19，000 - 21，000年的末次盛冰期，尽管平均条件较冷。因此，模拟表明，在东印度洋更大的冷却与强烈的上升流和浅温跃层，这是反映在古数据作为一个改变盆地范围（东西）的温度梯度。初步数据还显示，该地区的季节性和年与年之间的温度变化大大增加，这与有利于更强的海气相互作用的状态相一致。这段时间的气候模拟表明，这种变率的增加可能是由假设的“印度洋厄尔尼诺”的激活引起的。在整个项目中，研究人员将通过生成新的季节性和年度气候变化数据集以及研究新的模型模拟来进一步测试这一假设，这将有助于确定是否以及何时，这种模式将在未来出现。本项目建立在初步模型的基础上-数据调查表明，在过去的20年里，东印度洋的季节和年际气候变率急剧增强，冰川最大。这些数据表明，与未来预测相似的海洋条件变化可能导致印度洋出现目前未观测到的气候变率模式，类似于太平洋的现代厄尔尼诺现象。为了验证这一假设，研究人员将开发新的古气候数据集和模型分析，以探索印度洋在改变条件下的气候变化。拟议中的新的古数据将分离季节性和温跃层深度特征，从而更严格地检验“印度洋厄尔尼诺”假说。先进的模型代理比较技术，使用现有的和新的模型模拟从古气候模拟相互比较项目（PMIP）将开发进行额外的测试。将对历史观测和模式模拟进行分析，以确定这种模式是否与当今的气候变率不同，并解决与其前兆和背景条件有关的问题。这些问题也将利用耦合模式相互比较项目（CMIP）现有的和新的气候模式模拟进行探讨。这些模拟将被用来评估在不久的将来可能激活“印度洋厄尔尼诺”的不确定性。将利用模型-代用品比较的限制来确定是否可以减少这些不确定性。更广泛的影响包括学生和博士后培训，并支持亚利桑那大学的新教员。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This research will explore whether the Indian Ocean could sustain climate variability resembling El Nino under continued greenhouse warming. Testing this hypothesis is important because the activation of such a mode could drive large changes in year-to-year variability and hydrological extremes over the densely populated Indian Ocean rim. This mode of climate variability has not been observed in historical data, and therefore paleoclimate reconstructions are required to study conditions that favor its emergence, its spatial characteristics, and the ability of climate models to simulate it realistically. According to climate simulations, the activation of this mode depends on the state of the Indian Ocean, which currently does not exhibit upwelling nor has a shallow thermocline (the zone of the ocean water-column where temperatures rapidly decrease with depth) -- features needed to support strong, large-scale interactions between the ocean and atmosphere. Paleoclimate records indicate that these features could have existed in the geological past, particularly during the Last Glacial Maximum, roughly 19,000-21,000 years before present, albeit with cooler average conditions. Accordingly, simulations indicate greater cooling in the eastern Indian Ocean concurrent with strong upwelling and a shallow thermocline, which is reflected in the paleo-data as an altered basin-wide (east-west) temperature gradient. Preliminary data also reveal greatly increased seasonal and year-to-year temperature variations in this region, consistent with a state favoring stronger air-sea interactions. Climate simulations of this interval show that this increase in variability could have been caused by the activa- tion of the hypothesized "Indian Ocean El Nino". Throughout this project, the researchers will further test this hypothesis by generating new datasets of seasonal and year-to-year climate variability as well as investigating new model simulations that will help determine whether, and when, this mode will emerge in the future.This project builds on preliminary model-data investigations that indicate dramatically intensified seasonal and interannual climate variability in the eastern Indian Ocean during the Last Glacial Maximum. These data suggest that changes in oceanic conditions similar to those predicted for the future could cause the emergence of a presently unobserved mode of climate variability in the Indian Ocean that resembles modern El Nino in the Pacific. In order to test this hypothesis, the researchers will develop new paleoclimate datasets and model analyses to explore climate variability in the Indian Ocean under altered conditions. The proposed new paleodata will isolate seasonality and thermocline depth signatures and thus more rigorously test the "Indian Ocean El Nino" hypothesis. Advanced model-proxy comparison techniques using existing and new model simulations from the Paleoclimate Modelling Intercomparison Project (PMIP) will be developed to perform additional tests. Historical observations and model simulations will be analyzed to determine whether this mode is distinct from present-day climate variability, and address questions related to its precursors and background conditions under which it can become active. These questions will also be explored using existing and new climate model simulations from the Coupled Model Intercomparison Project (CMIP). These simulations will be used to assess uncertainties regarding the potential activation of the "Indian Ocean El Nino" in the near future. Constraints from the model-proxy comparison will be used to determine whether these uncertainties could be reduced. Further broader impacts include student and postdoc training, and support for a new faculty member at the University of Arizona.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.