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

地球？北极的冰冻圈具有很大的能力，可以通过温度反馈改变行星的反射率和表面温度，这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个机制组成的，这些机制的时间尺度从数小时到数千年不等，既可以在积雪中，也可以通过改变的冰冻圈覆盖。该项目旨在填补我们理解中的关键空白：1）像炭黑（BC）这样的吸光杂质如何通过对雪变质的影响来影响雪反馈，以及2）雪反馈中十年到几十年变化的来源以及为什么气候模型普遍低估1979年的解释？2008年北半球相对于遥感观测的负反馈（约2倍）。目标（1）的动机来自辐射建模和观测，表明BC在粗粒（老化）雪中干扰可见光的反射更多，这在近红外光谱中也更暗，表明BC在加速雪变质时触发至少两个正反射反馈机制。然而，杂质加热对变质作用的影响是不确定的。PI将使用一种新的近红外光学传感装置测量有和没有BC的积雪中雪有效粒度的演变，以确定BC对一种环境中变质作用的影响。目标（2）的动机是在模式反馈中观察到的偏差和初步分析，表明在瞬态气候模拟中有很大的几十年反馈变率。为了分离对气候反馈的贡献，并确定模式观测差异和反馈中的多年代变率的原因，他将把诊断性冰冻圈辐射强迫项纳入NCAR社区地球系统模式（CESM），并利用遥感和气候模式数据进行额外的分析。预计长期下降的反馈，与减少冰冻圈覆盖提示的问题：反馈达到峰值了吗？如果没有，什么时候可能，为什么？实现该项目的目标将使建模的反馈更一致的尺度，量化的气候和水文的影响，人为气溶胶排放更有信心，并提供一个机械的解释峰值反馈反馈的时间在一个变暖的世界。研究将紧密结合本科和研究生教育。雪杂质/变质实验和光学测量将是密歇根大学生物站（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，能量和示踪气体通量在站塔的测量，和数据解释。学生团队将部署在道格拉斯湖和其他地形在UMBS测量雪的属性和粒度的空间变异性的特点。这项活动将针对早期的本科生，以影响学位专业的选择和对科学职业道路的兴趣。参与老年人可以设计，建造和应用工程课程学分的现场仪器。冰冻圈的研究生课程？气候的相互作用将被纳入一个课程项目在PI？s courses.该项目产生的基础研究将提高对重要气候反馈过程的理解，工业排放如何影响这些过程，以及它们如何影响水资源。 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。

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.