Understanding the Influence of Climate Change on Temperature Persistence

温室气体排放造成的各种气候影响超出了全球气温升高的范围，其中许多影响，如热浪和极端降雨频率的增加，都是众所周知的。该奖项下的工作研究了尚未得到广泛认识的全球变暖的后果：短期地表温度波动持续较长时间的趋势。在20世纪和21世纪气候变化模拟的最后20年之间的比较中可以看到这种影响，地表温度异常的5天持续时间增加了50%。虽然该信号尚未在迄今为止的观测记录中被识别出来，但它是使用社区地球系统模型（CESM）进行的大量模型模拟的一个强大特征，并且可以在模型的各种简化配置中再现。这种持续增加的模式很有趣，因为它在海洋上比在陆地上更突出，尽管它延伸到澳大利亚、中国东部和加拿大西部。该奖项下的工作旨在根据一个概念模型来理解持久性的变化，在这个概念模型中，温度波动由随机强迫引起，并通过线性松弛而衰减。在这个模式中，持久性的增加是由于有效热容的增加、随机强迫的变红或控制弛豫的阻尼过程的减少。这项工作遵循两个流程，其中一个流程检查来自气候模式比对项目（CMIP）的再分析产品和模拟，特别是多模式大集合档案。另一个流包括使用社区大气模式（CAM， CESM的大气成分模式）的数值实验。一些实验涉及禁用相关反馈的技术，例如“云锁定”和在辐射代码中规定水蒸气。该项目利用了作为CESM代码库一部分可用的模型层次结构。这项工作具有社会意义，因为它有助于我们了解气候变化如何影响极端温度事件的持续，而这些事件的影响主要取决于它们的持续时间。研究小组还对当地的公立学校进行外展，为教师和学生提供一系列关于气候科学的外展讲座。此外，该项目还为两名研究生提供支持和培训。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。

Greenhouse gas emissions cause a variety of climatic effects which go beyond increasing global temperature and many of these, such as increases in the frequency of heat waves and extreme rainfall, are well recognized. Work under this award examines a consequence of global warming that has not been widely appreciated: the tendency for short-term surface temperature fluctuations to persist for longer periods of time. The effect has been seen in comparisons between the last two decades of the 20th and 21st centuries in climate change simulations, with increases of up to 50% in the 5-day persistence of surface temperature anomalies. While the signal has not been identified in the observed record to date it is a robust feature of simulations across a large ensemble of model simulations performed with the Community Earth System Model (CESM) and can be reproduced in a variety of simplified configurations of the model. The pattern of the persistence increase is intriguing as it is more prominent over the oceans than over land, although it extends over Australia, eastern China, and western Canada.Work under this award seeks to understand the change in persistence in terms of a conceptual model in which temperature fluctuations arise from random forcing and decay through linear relaxation. In this model an increase in persistence results from an increase in effective heat capacity, reddening of the stochastic forcing, or a decrease in the damping processes that control relaxation. The work follows two streams, one of which examines reanalysis products and simulations from the Climate Model Intercomparison Project (CMIP), particular the multi-model large ensemble archive. The other stream consists of numerical experiments using the Community Atmosphere Model (CAM, the atmospheric component model of CESM). Some experiments involve techniques to disable relevant feedbacks, for instance "cloud locking" and prescribing water vapor in the radiation code. The project takes advantage of the model hierarchy available as part of the CESM code base.The work has societal relevance as its serves to inform our understanding of how climate change influences the persistence of extreme temperature events, and the impacts of such events depends critically on their duration. The research team also conducts outreach to local public schools, providing a series of outreach lectures on climate science to teachers and students. In addition, the project provides support and training to two graduate students.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.