Collaborative Research: Evolving Hemispheric Albedo Asymmetry

合作研究：不断演变的半球反照率不对称性

• 批准号: 2233674
• 负责人: Daniel McCoy
• 金额: $ 2.22万
• 依托单位: University of Wyoming
• 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: 2023-02-01 至 2026-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2233674&HistoricalAwards=false
• 关键词: Collaborative; Research; Evolving; Hemispheric; Albedo

The albedo of the earth, meaning the fraction of incident sunlight that earth reflects back to space, is a critical control on the temperature of the planet, as higher albedo means less solar heating of the earth. Planetary albedo is a composite quantity determined by the reflection of sunlight from the relatively dark and thus low albedo ocean surface, lighter and thus higher albedo land surfaces, and the even higher albedos of snow and ice covered surfaces. Clouds add another layer of complexity as bright reflective clouds form intermittently over darker land and ocean. The complexity of planetary albedo is a challenge for efforts to determine the warming effect of greenhouse gas (GHG) increases since warming can cause a decrease in albedo, say due to the replacement of high-albedo sea ice with lower albedo ocean surface, which in turn can substantially enhance the GHG warming.Recent work shows that the albedos of the Northern and Southern Hemispheres are uncannily close: the sunlight received in each hemisphere is the same averaged over the year, and the amount reflected back to space is 99.7 watts per square meter in the Southern Hemisphere and 99.6 in the Northern Hemisphere (the resulting planetary albedo is about 29%). The sameness occurs despite the higher albedo of the Northern Hemisphere due to its larger land area, which yields a difference in hemispheric reflected sunlight of about 6 watts per square meter under clear skies. This difference must be compensated by clouds, and the work of Datseris and Stevens (2021) shows that the compensation is largely occurring over the middle- and high-latitude oceans, as the Southern Ocean is cloudier than the northern Pacific and Atlantic by about 11%. Datseris and Stevens also show that while planetary albedo has decreased appreciably over the past two decades the Northern and Southern Hemispheres have seen equivalent reductions, thereby retaining their "albedo symmetry". There is no theory for why clouds should compensate for surface albedo differences, and it is of course possible that the albedo symmetry of the recent record is a coincidence and not the result of a global-scale adjustment mechanism.Work under this award seeks to determine if an adjustment mechanism exists and if so to develop a theory for it. In addition to observational data from satellite missions and reanalysis products the work takes advantage of large ensembles of model simulations including simulations from the Coupled Model Intercomparison Project and a recent perturbed physics ensemble (PPE) created using the Community Atmosphere Model (CAM, the atmospheric component model of CESM, the Community Earth System Model). Results from analysis of these models are used to design additional simulations created with CAM, CESM, and a simplified version of CESM in which the ocean component model is replaced by a thermodynamic "slab" which simulates ocean heat storage but not ocean circulation. The work is of societal as well as scientific interest given the potentially large role that albedo changes could play in determining how much warming is caused by a given increase in GHG concentrations. A theory of albedo adjustment operating through cloud processes and on a global basis could provide valuable guidance in anticipating the magnitude of future climate change. The project also provides support and training for two graduate students, thereby providing for the future scientific work force in this research area. Undergraduate students are also involved in the project as summer interns.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.

地球的反照率，即地球反射回太空的入射阳光的比例，是对地球温度的关键控制，因为反照率越高意味着地球受到的太阳加热就越少。 行星反照率是一个综合量，由相对较暗且反照率较低的海洋表面、较亮且反照率较高的陆地表面以及雪和冰覆盖的表面的反照率更高的太阳光反射决定。 明亮的反光云在较暗的陆地和海洋上空间歇性地形成，云层又增加了一层复杂性。 行星反照率的复杂性对于确定温室气体（GHG）增加的变暖效应的努力来说是一个挑战，因为变暖可能导致反照率降低，例如由于高反照率海冰被反照率较低的海洋表面取代，这在最近的研究表明，北半球和南半球的反照率惊人地接近：每个半球全年平均接收到的阳光是相同的，反射回地球的量南半球的太空能量为每平方米 99.7 瓦，北半球为每平方米 99.6 瓦（由此产生的行星反照率约为 29%）。 尽管北半球由于陆地面积较大而具有较高的反照率，但在晴朗的天空下，半球反射的阳光会产生每平方米约 6 瓦的差异，但这种情况仍然存在。这种差异必须通过云来补偿，Datseris 和 Stevens (2021) 的工作表明，补偿主要发生在中高纬度海洋，因为南大洋比北太平洋和大西洋多云约 11 %。 达瑟里斯和史蒂文斯还表明，虽然过去二十年行星反照率明显下降，但北半球和南半球也出现了同等的下降，从而保持了它们的“反照率对称性”。 没有任何理论可以解释为什么云应该补偿地表反照率差异，当然最近记录的反照率对称性也有可能是巧合，而不是全球范围调整机制的结果。该奖项下的工作旨在确定是否存在调整机制，如果存在，则为其制定理论。 除了来自卫星任务和再分析产品的观测数据之外，这项工作还利用了大型模型模拟集合，包括耦合模型比对项目的模拟和最近使用社区大气模型（CAM，大气成分）创建的扰动物理集合（PPE） CESM（社区地球系统模型）模型。 这些模型的分析结果用于设计由 CAM、CESM 和 CESM 的简化版本创建的附加模拟，其中海洋成分模型被热力学“板”取代，该热力学“板”模拟海洋热存储，但不模拟海洋环流。这项工作具有社会和科学意义，因为反照率变化在确定温室气体浓度一定增加所导致的变暖程度方面可能发挥重要作用。通过云过程并在全球范围内运行的反照率调整理论可以为预测未来气候变化的严重程度提供有价值的指导。 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。 本科生也以暑期实习生的身份参与该项目。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标准进行评估，被认为值得支持。