RAPID: Detectability of Changes in the Walker Circulation in Response to Global Warming

RAPID：沃克循环变化响应全球变暖的可检测性

• 批准号: 1203754
• 负责人: Pedro Di Nezio
• 金额: $ 3万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2013-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1203754&HistoricalAwards=false
• 关键词: RAPID; Detectability; Changes; Walker; Circulation

This is one of 16 Rapid Response (RAPID) projects funded as the result of a Dear Colleague Letter (NSF 11-006) encouraging diagnostic analyses of climate model simulations prepared for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Research conducted in these projects is expected to lead to more detailed model intercomparisons, better understanding of robust model behaviors, and better understanding and quantification of uncertainty in future climate simulations.The Walker circulation is an east-west overturning circulation that spans the equatorial Pacific Ocean, associated with low sea level pressure (SLP) over the western Pacific and the Maritime Continent and higher SLP in the eastern equatorial Pacific. Variability of the strength of the Walker cell is a dominant form of climate variability in the tropics, associated with large-scale fluctuations in rainfall and other climatic variables, and secular change in the Walker cell forced by global warming would likely have the same consequences.Work performed here examines the response of the Walker circulation to global warming in 20th century climate simulations performed for the AR5, and compares model simulations with available observations. Previous work has shown that model simulations are generally consistent with the observed small reduction of the east-west sea level pressure (SLP) gradient across the equatorial pacific over the 20th century, which indicates a slight weakening of the Walker circulation. But several issues remain to be addressed: 1) the weakening of the Walker circulation depends on the sensitivity of global mean precipitation to warming, for which there is no agreement between climate models and observations over the recent past; 2) it is not clear whether the signature of the observed warming is El Nino-like or La Nina-like, which has implications for the east-west equatorial SLP trend; 3) it is possible that the observed changes in the SLP gradient are a spurious trend associated with the strong low frequency variability of the Pacific basin. To address these issues, the PI would conduct a model-observation comparison of linear trends in the following variables during the 20th century: the east-west SLP gradient, tropical-mean precipitation, tropical-mean water vapor content, the east-west sea surface temperature gradient, the tilt of the thermocline, and the thermal stratification of the equatorial Pacific Ocean. Where possible, multiple simulations from the same model would be used to assess the potential contribution of natural variability to the 20th-century trends.The broader impact of the project lies in its support of the IPCC AR5, which is intended to provide information on climate change and its consequences to decision makers worldwide. Walker cell variability plays a dominant role in the variability of tropical climate, affecting the distribution of rainfall and other climatic variables over heavily populated and climatically sensitive regions worldwide. Changes in the Walker cell due to global warming would likely have the same effects. Research conducted here regarding the extent to which the observed changes in the Walker cell constitute natural variability or warming-induced change, and the extent to which climate model simulations can accurately portray the fundamental mechanisms producing the changes, could thus have important implications for decision makers concerned with the implications of tropical climate change.

这是一封亲爱同事的信 (NSF 11-006) 资助的 16 个快速响应 (RAPID) 项目之一，鼓励对为政府间气候变化专门委员会第五次评估报告 (IPCC AR5) 准备的气候模型模拟进行诊断分析。这些项目中进行的研究预计将导致更详细的模型相互比较，更好地理解稳健的模型行为，以及更好地理解和量化未来气候模拟中的不确定性。沃克环流是横跨赤道太平洋的东西向翻转环流，与西太平洋和海洋大陆的低海平面气压（SLP）以及赤道东太平洋的较高海平面气压有关。 沃克环流强度的变化是热带地区气候变化的主要形式，与降雨量和其他气候变量的大规模波动有关，而全球变暖迫使沃克环流的长期变化可能会产生相同的后果。这里进行的工作检查了 AR5 进行的 20 世纪气候模拟中沃克环流对全球变暖的响应，并将模型模拟与现有观测结果进行比较。 先前的工作表明，模型模拟与观察到的20世纪赤道太平洋东西海平面压力（SLP）梯度小幅减小基本一致，这表明沃克环流略有减弱。 但仍有几个问题有待解决：1）沃克环流的减弱取决于全球平均降水量对变暖的敏感性，而气候模型和最近的观测结果之间并没有达成一致； 2）尚不清楚观测到的变暖特征是类厄尔尼诺现象还是类拉尼娜现象，这对赤道东西向海平面气压趋势有影响； 3）观测到的SLP梯度变化可能是与太平洋盆地强烈的低频变化相关的虚假趋势。 为了解决这些问题，PI将对20世纪以下变量的线性趋势进行模型观测比较：东西向海平面气压梯度、热带平均降水量、热带平均水汽含量、东西向海洋表面温度梯度、温跃层倾斜以及赤道太平洋的热层化。 在可能的情况下，将使用同一模型的多次模拟来评估自然变率对 20 世纪趋势的潜在贡献。该项目的更广泛影响在于其对 IPCC AR5 的支持，该报告旨在提供有关气候的信息变化及其对全世界决策者的影响。 沃克细胞变异在热带气候的变异中起着主导作用，影响全球人口稠密和气候敏感地区的降雨量和其他气候变量的分布。 全球变暖导致沃克细胞的变化可能会产生相同的影响。 这里进行的研究涉及沃克细胞中观察到的变化在多大程度上构成自然变异或变暖引起的变化，以及气候模型模拟可以在多大程度上准确描述产生变化的基本机制，因此可能对决策者产生重要影响关注热带气候变化的影响。