Collaborative Research: Understanding the Links between Tropical Cyclones and Tropical Circulation under Climate Change through Idealized Coupled Climate Modeling

合作研究：通过理想化耦合气候模型了解气候变化下热带气旋与热带环流之间的联系

• 批准号: 2327958
• 负责人: Kevin Reed
• 金额: $ 67.78万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-11-15 至 2026-10-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2327958&HistoricalAwards=false
• 关键词: Collaborative; Research; Understanding; Links; between

Tropical cyclones (TCs), including the hurricanes of the Atlantic and Caribbean, derive their destructive power from the heat of the ocean beneath them. The fueling of TCs by warm sea surface temperatures (SSTs) thus suggests that the warming of the oceans by greenhouse gas emissions should bring more frequent and more damaging TCs. One part of this expectation holds true: the strongest TCs have become even stronger in recent decades, in agreement with model simulations and theoretical arguments. But there is no satisfactory theory for how TC frequency will change in a warming world and model-based studies have shown mixed results. The recent study of Chand et al. (2022) shows a decline in TC numbers which the authors attribute to a reduction in the strength of the the north-south oriented Hadley cell and the east-west oriented Walker cell. The former features rising air over the warm SSTs of the deep tropics and subsidence over the cooler subtropics, while the latter features convection over the "warm pool" of the tropical western Pacific and subsidence over eastern Pacific "cold tongue". But other studies suggests that reductions in overturning strength should result in an increase in the number of TCs rather than a decrease.Research under this award considers the role of the overturning cells in setting TC frequency and other aggregate properties and the consequences for TC behavior of changes in overturning due to greenhouse warming. The work is conducted using two idealized configurations of the Community Earth System Model (CESM) which are designed to isolate the mechanisms of interest and study them in their simplest form. The first configuration is an "aquaplanet", with an atmosphere coupled to a dynamic ocean model but no land surface. In this configuration there is no equivalent of the Pacific warm pool and cold tongue and hence no analog for the Walker cell, although the SST contrast between lower and higher latitudes still produces a Hadley cell. The second is a "ridge" configuration, in which a narrow oceanic ridge stands in for the American landmass that separates the tropical Atlantic and Pacific Oceans. The ocean dynamics created by the imposition of a north-south ridge creates a contrast between cooler surface water to the west of the ridge and warmer SST to the east, which in turn induces a Walker circulation. These configurations are augmented by simulations at higher resolution (0.25 degree grid spacing) which are better able to capture TC behavior. For reasons of computational cost the high-resolution simulations use a motionless "slab" ocean in which the SST contrasts generated by the aquaplanet and ridge configurations are imposed indirectly so as not to compromise heat transfer from the ocean to the TCs.The work is of societal as well as scientific interest given the tremendous destructive power of TCs and the need to assess changes in TC risk due to greenhouse warming. The work also has scientific broader impacts through the addition of new configurations to the CESM model hierarchy. The model versions developed in this project will be made available to the research community through the Simpler Models web portal (www.cesm.ucar.edu/models/simple) and will be supported with documentation and reference simulations. In addition, the project provides support and training to two graduate students, thereby providing for the future scientific workforce in this research area.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.

热带气旋 (TC)，包括大西洋和加勒比海的飓风，其破坏力来自其下方海洋的热量。 因此，温暖的海面温度（SST）对热带气旋的助推作用表明，温室气体排放导致的海洋变暖应该会带来更频繁、更具破坏性的热带气旋。 这一预期的一部分是正确的：近几十年来，最强的TC变得更加强大，这与模型模拟和理论论证相一致。但对于气候变暖的世界中热带气旋频率如何变化，目前还没有令人满意的理论，基于模型的研究显示出不同的结果。 Chand 等人的最新研究。 (2022) 显示 TC 数量下降，作者将其归因于南北向的哈德利环流和东西向的沃克环流强度的减弱。 前者的特点是深热带温暖的海温上空上升和较冷的亚热带上空的沉降，而后者的特点是热带西太平洋“暖池”上空的对流和东太平洋“冷舌”上空的沉降。但其他研究表明，倾覆强度的降低应该会导致 TC 数量的增加而不是减少。该奖项下的研究考虑了倾覆单元在设定 TC 频率和其他聚合特性中的作用，以及对 TC 行为的影响。由于温室变暖导致的倾覆变化。这项工作是使用社区地球系统模型（CESM）的两种理想化配置进行的，这些配置旨在隔离感兴趣的机制并以最简单的形式研究它们。 第一种配置是“水上行星”，其大气层与动态海洋模型耦合，但没有陆地表面。 在这种配置中，没有太平洋暖池和冷舌的对应物，因此没有沃克环流的类似物，尽管低纬度和高纬度之间的海温对比仍然产生哈德利环流。 第二种是“山脊”结构，其中一条狭窄的洋脊代表分隔热带大西洋和太平洋的美洲大陆。 南北洋脊所产生的海洋动力在洋脊以西较冷的地表水与东部较温暖的海表温度之间形成对比，进而引发沃克环流。 这些配置通过更高分辨率（0.25 度网格间距）的模拟得到增强，能够更好地捕获 TC 行为。出于计算成本的原因，高分辨率模拟使用静止的“板状”海洋，其中间接施加由水行星和山脊配置产生的海温对比，以免影响从海洋到TC的热传递。这项工作是鉴于热带气旋具有巨大的破坏力，并且需要评估温室变暖导致的热带气旋风险变化，因此引起了社会和科学的兴趣。 通过向 CESM 模型层次结构添加新配置，这项工作还具有更广泛的科学影响。该项目开发的模型版本将通过 Simpler Models 门户网站 (www.cesm.ucar.edu/models/simple) 提供给研究界，并将得到文档和参考模拟的支持。 此外，该项目还为两名研究生提供支持和培训，从而为该研究领域的未来科学劳动力提供支持。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查进行评估，认为值得支持标准。