Collaborative Research: P2C2--A Model/Proxy Synthesis of Walker Circulation Trends During the Last Millennium

太平洋沃克环流改变了世界各地的极端天气和气候，但其对外部气候强迫的敏感性尚不清楚。特别是，对20世纪Walker环流趋势的观测估计提供了相互矛盾的结果，一些人认为有加强趋势，另一些人认为有减弱趋势或没有趋势，这使得将这些趋势归因于任何特定的强迫变得复杂。古气候记录可以通过提供长期背景来改进趋势的探测和归因，但由于缺乏覆盖过去千年的多代理综合产品和气候模式模拟，古气候记录的使用受到阻碍。该项目旨在使用最近构建的PAGES Iso2k数据库创建多个Walker循环指标的新的定量重建，并使用群落地球系统模型最后千年集合（LME）及其同位素激活补充（iLME）的新模拟来评估这些指标的变化机制和趋势。该研究试图应用这些新工具来回答一个核心问题：从上个千年到20世纪，沃克环流变化和趋势的机制是什么？外部强迫和内部变率的相对作用是什么？潜在的广泛影响包括强大的科学和教育方面。热带太平洋的气候变率影响社会和生态系统；因此，了解沃克环流的长期变率对于改善对21世纪气候变化影响的预估至关重要。这个科学跨学科的研究团队全部由早期职业研究人员组成，其中两名是女性。该项目将资助一名研究生和博士后研究员。来自弱势群体的高中生将被招募参加暑期实习，并通过一个针对STEM多样性的项目获得指导。最后，该项目将产生热带太平洋气候变率和iLME集合成员的多代理综合重建，所有这些都将作为资源提供给更广泛的科学界和民间团体。该奖项反映了美国国家科学基金会的法定使命，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。

The Pacific Walker circulation alters weather and climate extremes around the world, but its sensitivity to external climate forcings remains unknown. In particular, observational estimates of 20th century trends in the Walker circulation provide conflicting results, with some suggesting a strengthening and others a weakening or no trend, complicating the attribution of these trends to any specific forcing. Paleoclimate records can improve the detection and attribution of trends by providing longer-term context, but their use has been hindered by the lack of multi-proxy synthesis products and climate model simulations covering the last millennium. This project aims to create new quantitative reconstructions of multiple Walker circulation metrics using the recently constructed PAGES Iso2k database, and to evaluate the mechanisms for variability and trends in these metrics using the Community Earth System Model Last Millennium Ensemble (LME) and new simulations with its isotope-enabled complement (iLME). The research seeks to apply these new tools to answer one central question: What are the mechanisms underlying Walker circulation variability and trends from the Last Millennium through the 20th century, and what are the relative roles of external forcings and internal variability?The potential Broader Impacts (B.I.) includes strong science and educational aspects. Climate variability in the tropical Pacific affects societies and ecosystems; understanding long-term variability of the Walker circulation is thus critical for improving projections of the impacts of 21st century climate change. This scientifically-interdisciplinary research team is composed entirely of early-career researchers, two of whom are female. The project will support a graduate student and postdoctoral researcher. High school students from underrepresented demographics will be recruited for summer internships and mentoring through a program that targets diversity in STEM. Finally, the project will produce multi-proxy synthesis reconstructions of tropical Pacific climate variability and iLME ensemble members, all of which will be made available as resources to the wider scientific and civil communities.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.