CAREER: Linking cryospheric processes across scales to model non-linear albedo feedback

职业：跨尺度连接冰冻圈过程以模拟非线性反照率反馈

• 批准号: 1253154
• 负责人: Mark Flanner
• 金额: $ 60.15万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-05-01 至 2020-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1253154&HistoricalAwards=false
• 关键词: CAREER; Linking; cryospheric; processes; across

Earth?s cryosphere holds large capacity to alter planetary reflectance and surface temperature through albedo feedback, partially explaining the high sensitivity of Arctic climate. Albedo feedback, however, is actually composed of multiple mechanisms operating on timescales ranging from hours to millennia, both within snowpack and via altered cryospheric cover. This project aims to fill crucial gaps in our understanding of: 1) how light-absorbing impurities like black carbon (BC) influence albedo feedback via their effect on snow metamorphism, and 2) sources of decadal to multi-decadal variability in albedo feedback and explanation of why climate models universally underestimate 1979?2008 boreal albedo feedback (by ~2-fold) relative to remote sensing observations. Motivation for goal (1) arises from radiative modeling and observations showing that BC perturbs visible albedo more in coarser-grained (aged) snow, which is also darker in the near-infrared spectrum, indicating that BC triggers at least two positive albedo feedback mechanisms when it accelerates snow metamorphism. The influence of impurity heating on metamorphism, however, is uncertain. The PI will measure the evolution of snow effective grain size in snowpacks generated with and without BC, using a new near-infrared optical sensing device, to determine BC influence on metamorphism in one environment. Goal (2) is motivated by the observed bias in model feedback and a preliminary analysis showing large multi-decadal feedback variability in transient climate simulations. To isolate contributions to albedo feedback and identify causes of model-observation discrepancy and multi- decadal variability in feedback, he will incorporate diagnostic cryosphere radiative forcing terms into the NCAR Community Earth System Model (CESM) and conduct additional analyses with remote sensing and climate model data. Expectation of a long-term decline in albedo feedback associated with reduced cryospheric cover prompts the questions: Has albedo feedback peaked? If not, when might it, and why? Attaining the project objectives will enable modeling albedo feedback more consistently across scales, quantifying climate and hydrological influences of anthropogenic aerosol emissions more confidently, and providing a mechanistic explanation for the timing of peak albedo feedback in a warming world.Research will be tightly integrated with undergraduate and graduate education. Snow impurity/metamorphism experiments and optical measurements will be part of a weekend research experience designed for freshmen at the University of Michigan Biological Station (UMBS). Students will gain exposure to winter field methods, instrumentation, measurements of energy and trace gas fluxes at station towers, and data interpretation. Student teams will deploy on Lake Douglas and other terrain at UMBS to measure snow properties and characterize spatial variability in grain size. This activity will be targeted toward early undergraduate students to influence degree major choices and interest in science career paths. Participating seniors may design, build, and apply field instruments for engineering course credit. Graduate studies of cryosphere?climate interactions will be incorporated into a course project in one of the PI?s courses. The fundamental research resulting from this project will enhance understanding of important climate feedback processes, how industrial emissions influence these processes, and how they may impact water resources. The integration of this research with educational activities will contribute to the training of the next generation of geoscientists and engineers.

地球冰冻圈具有通过反照率反馈改变行星反射率和表面温度的巨大能力，部分解释了北极气候的高敏感性。然而，反照率反馈实际上是由多种机制组成，其运行时间尺度从几小时到几千年不等，无论是在积雪内还是通过改变的冰冻圈覆盖层。该项目旨在填补我们理解中的关键空白：1）像黑碳（BC）这样的光吸收杂质如何通过对雪变质作用的影响来影响反照率反馈，2）反照率反馈和数十年变化的来源和解释为什么气候模型普遍低估 1979 年至 2008 年相对于遥感观测的北方反照率反馈（约 2 倍）。目标 (1) 的动机源于辐射模型和观察结果，表明 BC 在粗粒（老化）雪中对可见反照率的扰动更大，在近红外光谱中也更暗，这表明 BC 触发至少两种正反照率反馈机制当它加速雪的变质作用时。然而，杂质加热对变质作用的影响尚不确定。 PI将使用一种新的近红外光学传感装置来测量有和没有BC生成的雪堆中雪有效颗粒尺寸的演变，以确定BC对一种环境中变质作用的影响。目标 (2) 的动机是模型反馈中观察到的偏差以及显示瞬态气候模拟中存在较大的数十年反馈变异性的初步分析。为了隔离对反照率反馈的贡献并确定模型观测差异和反馈中的数十年变化的原因，他将把诊断性冰冻圈辐射强迫项纳入 NCAR 社区地球系统模型 (CESM)，并利用遥感和气候模型进行额外分析数据。与冰冻圈覆盖减少相关的反照率反馈长期下降的预期引发了以下问题：反照率反馈是否已达到峰值？如果不是，什么时候可以，为什么？实现项目目标将使反照率反馈在不同尺度上更加一致地建模，更加自信地量化人为气溶胶排放的气候和水文影响，并为变暖世界中反照率峰值反馈的时间提供机械解释。研究将与本科生紧密结合和研究生教育。雪杂质/变质实验和光学测量将成为密歇根大学生物站 (UMBS) 为新生设计的周末研究体验的一部分。学生将接触到冬季现场方法、仪器、站塔能量和微量气体通量的测量以及数据解释。学生团队将部署在道格拉斯湖和 UMBS 的其他地形上，以测量雪的特性并表征颗粒尺寸的空间变化。这项活动将针对早期本科生，以影响学位专业的选择和对科学职业道路的兴趣。参与的高年级学生可以设计、建造和应用现场仪器以获得工程课程学分。冰冻圈与气候相互作用的研究生研究将被纳入 PI 课程的课程项目中。该项目的基础研究将增强对重要气候反馈过程、工业排放如何影响这些过程以及它们如何影响水资源的理解。 这项研究与教育活动的结合将有助于培养下一代地球科学家和工程师。

项目成果

SNICAR-ADv3: a community tool for modeling spectral snow albedo

SNICAR-ADv3：用于建模光谱雪反照率的社区工具

• DOI: 10.5194/gmd-14-7673-2021
• 发表时间: 2021-01
• 期刊: Geoscientific Model Development
• 影响因子: 5.1
• 作者: Flanner, Mark G.;Arnheim, Julian B.;Cook, Joseph M.;Dang, Cheng;He, Cenlin;Huang, Xianglei;Singh, Deepak;Skiles, S. McKenzie;Whicker, Chloe A.;Zender, Charles S.
• 通讯作者: Zender, Charles S.