Modeling the Tropical Atmosphere-Ocean System: Determining the Causes of Near Future Subtropical Drying

热带大气-海洋系统建模：确定近期亚热带干燥的原因

• 批准号: 0804107
• 负责人: Richard Seager
• 金额: $ 54.33万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804107&HistoricalAwards=false
• 关键词: Modeling; Tropical; Atmosphere; Ocean; System

Drying of the subtropics is a ubiquitous and robust result within model projections of 21st century climate. This drying impacts several areas with important agricultural economies and rising populations, most notably northern Mexico, the southwestern United States, southern Europe, North Africa and the Middle East. According to the models, this drying sets in immediately in the future. The projected amplitude is such that the U.S. Southwest will go over to a permanent Dust Bowl or 1950s drought level of aridity in the next few years to decades. While the future drought raises the specter of a return of conditions akin to Medieval mega droughts those have been linked to persistent La Nina-like states but future droughts appear to be a result of general warming.Research will be conducted to determine the causes of the drying of the Southwest and the subtropics using coupled General Circulation Models (GCMs) and simplified models. Both thermodynamic changes - whereby rising humidity leads to amplification of existing patterns of water vapor transport by the mean circulation, making dry areas drier and wet areas wetter - and changes in atmospheric circulation that shift patterns of precipitation and evaporation are involved. The investigators will a) determine within coupled GCMs the relative contributions of thermodynamical and dynamical mechanisms to subtropical drying and what changes in atmospheric circulation (MMC, transient eddies and stationary waves) are responsible for the dynamical contribution to drying indifferent areas,b) use diagnoses of coupled GCM and a hierarchy of simplified models to determine the causes of the changes in atmospheric circulation, examine the impacts of changes in tropical and extratropical SSTs and tropospheric temperatures, and study low level warming at higher latitudes and stratospheric cooling,c) determine the interactions between eddies, the mean circulation and water vapor transports that underlie shifts in precipitation and evaporation zones and subtropical drying, examining both winter and summer seasons, and d) contrast the dynamics of tropical forcing of naturally-occurring droughts with the dynamics of anthropogenic drought as a means to identify the causes of current and future drought.Intellectual merit of the research comes from understanding the fundamentals of how the tropical and global atmosphere circulation and hydrological cycle respond to external forcing which will lead to an improved understanding of the general circulation, in particular, the interactions between eddies, the mean flow and moist processes.Broader implications of the research concern the future of water resources in the arid lands of North America. The work will improve understanding of model projections of human-induced climate change and subtropical drying and, hence, aid assigning of confidence to the predictions. The PIs will communicate results to the climate research community and also to those making water-related decisions and work to educate a wider public on these matters through publications, open addresses, the media and the internet.

亚热带干旱是 21 世纪气候模型预测中普遍存在且强有力的结果。这种干燥影响了一些农业经济重要且人口不断增长的地区，尤其是墨西哥北部、美国西南部、欧洲南部、北非和中东。根据模型，这种干燥会在未来立即发生。预计美国西南部地区将在未来几年到几十年内进入永久性沙尘暴或 20 世纪 50 年代干旱水平。虽然未来的干旱引发了类似中世纪特大干旱的担忧，这些干旱与持续的拉尼娜状态有关，但未来的干旱似乎是普遍变暖的结果。将进行研究以确定干旱的原因使用耦合大气环流模型 (GCM) 和简化模型研究西南地区和亚热带地区的干燥情况。热力学变化（湿度上升导致平均环流放大现有的水蒸气输送模式，使干燥地区更干燥，潮湿地区更湿润）和大气环流变化（改变降水和蒸发模式）都参与其中。研究人员将 a) 在耦合 GCM 内确定热力学和动力学机制对亚热带干燥的相对贡献，以及大气环流的哪些变化（MMC、瞬变涡流和驻波）对不同地区干燥的动力学贡献负责，b) 使用诊断耦合 GCM 和一系列简化模型，以确定大气环流变化的原因，检查热带和温带海温和对流层温度变化的影响，并研究高纬度地区的低层变暖c) 确定涡流、平均环流和水汽输送之间的相互作用，这些是降水和蒸发区变化以及亚热带干燥的基础，检查冬季和夏季，以及 d) 对比热带自然强迫的动态以人为干旱动态作为确定当前和未来干旱原因的手段。该研究的学术价值来自于了解热带和全球大气环流和水文循环如何响应的基本原理外部强迫将导致更好地了解大气环流，特别是涡流、平均流和潮湿过程之间的相互作用。这项研究的更广泛影响涉及北美干旱地区水资源的未来。这项工作将增进对人为气候变化和亚热带干燥的模型预测的理解，从而帮助确定预测的置信度。 PI 将向气候研究界以及做出与水相关决策的人员传达结果，并努力通过出版物、公开演讲、媒体和互联网对更广泛的公众进行有关这些问题的教育。