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Collaborative Research: Evolving Hemispheric Albedo Asymmetry

合作研究：不断演变的半球反照率不对称性

基本信息

批准号：
2233673
负责人：
Maria Rugenstein
金额：
$ 64.28万
依托单位：
Colorado State University
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=2233673&HistoricalAwards=false
关键词：
Collaborative Research Evolving Hemispheric Albedo

项目摘要

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太阳光的比例，是对地球温度的关键控制，因为更高的反照率意味着地球的太阳加热更少。行星反照率是一个综合量，由相对较暗的低反照率海洋表面、较轻的反照率较高的陆地表面以及覆盖的雪和冰表面的反照率更高的阳光的反射确定。云层增加了另一层复杂性，因为明亮的反射云间歇性地在较暗的陆地和海洋上形成。行星反照率的复杂性对确定温室气体(GHG)增加的变暖效应是一个挑战，因为气候变暖会导致反照率下降，这是因为高反照率的海冰被低反照率的海洋表面取代，从而大大增强了温室气体变暖。最近的研究表明，南北半球的反照率惊人地接近：两个半球接收的太阳光全年平均相同，反射回太空的量在南半球为99.7瓦/平方米，在北半球为99.6瓦/平方米(由此产生的行星反照率约为29%)。尽管北半球的反照率较高，因为其陆地面积较大，在晴朗的天空下，半球反射的阳光相差约每平方米6瓦，但这种情况仍然存在。这一差异必须由云来补偿，Datseris和Stevens(2021年)的工作表明，补偿主要发生在中高纬度海洋上，因为南大洋的云量比北太平洋和大西洋多11%左右。Datseris和Stevens还表明，虽然行星的反照率在过去20年中显著下降，但南北半球的反照率也出现了同样的下降，从而保持了它们的“反照率对称性”。没有理论可以解释为什么云层应该补偿地表反照率的差异，当然，最近记录的反照率对称性也可能是巧合，而不是全球尺度调整机制的结果。该奖项的工作旨在确定是否存在调整机制，如果存在，则为其发展一种理论。除了来自卫星飞行任务和再分析产品的观测数据外，这项工作还利用了大量的模型模拟，包括耦合模式相互比较项目的模拟和最近利用共同体大气模型(CAM，欧洲空间物理中心的大气成分模型，共同体地球系统模型)创建的扰动物理系综。这些模型的分析结果被用来设计用CAM、CESM和CESM的简化版本创建的附加模拟，在CESM的简化版本中，海洋成分模型被模拟海洋储热而不是海洋环流的热力学“平板”取代。鉴于反照率变化可能在确定温室气体浓度的增加在多大程度上导致变暖方面发挥潜在的巨大作用，这项工作具有社会和科学意义。通过云过程和在全球范围内运作的反照率调整理论可以为预测未来气候变化的规模提供宝贵的指导。该项目还为两名研究生提供了支持和培训，从而为这一研究领域未来的科学工作提供了支持。本科生也作为暑期实习生参与了该项目。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。