Collaborative Research: Assessing the Simulated Arctic Freshwater System in CMIP5 Models, the CESM Large Ensemble, and Forced Simulations

北极淡水系统可能在未来几十年经历相当大的变化，对海洋环流、气候和生态系统产生下游影响。了解和预测这些影响的能力反过来将对渔业、能源分配和再保险业等产生重要的社会经济影响。然而，气候预测的可靠性是不确定的，人们对自然变异性在人类强迫变化中的重要性的了解也是有限的。该项目力求通过一系列模拟实验以及将模型结果与观测和再分析数据集进行比较来解决这些问题。该项目将通过支持年轻的、职业生涯早期的女性PI在其职业生涯的形成阶段以及对研究生培训的支持来促进STEM劳动力的发展。国际和平协会将利用她与国家大气研究中心的关系，将项目成果纳入其面向公众的外联展览中。该项目将调查以下主要科学问题：1.气候模型是否显示了21世纪及以后北冰洋净水变化的一致图景？模型差异是否有明显的原因(例如，分辨率、海冰模型的复杂性、通过加拿大北极群岛的海峡数量等)？2.北极净水预算不同条款的内部变化在气候模拟中的作用有多大？这对不同时间尺度的未来预测的不确定性有何影响？一个集合需要多大才能捕捉到内部变化的大小？3.在弗拉姆海峡和开关站区域模拟的FW分量与过去十年的观测结果吻合程度如何？导致不同来源的淡水预算变化的动力是什么？为了解决这些问题，首先将评估耦合模式相互比较项目第五阶段(CMIP5)对20世纪和21世纪北冰洋淡水预算的模拟，然后分析来自共同体地球系统模型(CESM)的大量模拟中北极淡水预算条款的内部变化的作用。最后，将来自弗拉姆海峡和北极开关站地区不同来源的FW的贡献与使用新的模拟FW示踪剂的观测结果进行比较，并将研究导致不同来源FW变化的北冰洋动力。参加CMIP5的新一代气候模型的北冰洋净水预算尚未进行分析，尽管与CMIP3相比，由于北冰洋海冰模拟的改进和加拿大北极群岛增加的开放航道，北冰洋净水预算可能会发生变化。大型CESM集合的使用提供了一个独特的机会来评估内部变化在北极净水预算中的作用，与CMIP5的跨模型分散进行比较将使人们能够深入了解未来预测中的不确定性来源。此外，在CESM中使用FW示踪剂将允许与一组新的观测进行更详细的比较，并将能够分析导致北极两个关键区域不同来源的FW年际变化的动态。

The Arctic freshwater (FW) system is likely to undergo considerable change in coming decades with downstream impacts on ocean circulation, climate, and ecosystems. An ability to understand and project these impacts, in turn, will have important socio-economic influences on fisheries, energy distribution, and reinsurance industries, amongst others. However, the reliability of climate projections is uncertain and there is only a limited understanding of the importance of natural variability in the midst of anthropogenically forced change. This project seeks to address these issues through a series of modeling experiments and comparison of the model results with observational and reanalysis data sets. This project will contribute to STEM workforce development through provision of support to a young, early-career, female PI during the formative years of her career and support for the training of a graduate student. The PI will leverage her connections with the National Center for Atmospheric Research to include project results in their outreach exhibits for the general public. Results will also be included in public talks and university lectures.This project will investigate the following major science questions:1. Do climate models show a consistent picture of projected Arctic Ocean FW changes during the 21st century and beyond? Are there obvious reasons for the model differences (e.g., resolution, sea ice model complexity, number of straits through the Canadian Arctic Archipelago, etc.)?2. How large is the role of internal variability for different terms of the Arctic FW budget in climate simulations? How does this affect uncertainty in future projections at various timescales? How large does an ensemble need to be in order to capture the magnitude of internal variability?3. How well do simulated FW components in Fram Strait and the switchyard region agree with observations from the last decade? What are the dynamics that lead to changes in FW from different sources?To address these questions, first the Arctic Ocean freshwater (FW) budget in the suite of the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations for the 20th and 21st century will be assessed, followed by an analysis of the role of internal variability of terms of the Arctic FW budget in a large ensemble of simulations from the Community Earth System Model (CESM). Finally, the contribution of FW from different sources in Fram Strait and the Arctic switchyard region in the CESM will be compared with observations using new simulated FW tracers, and the Arctic Ocean dynamics leading to the variability of FW from different sources will be investigated. The Arctic Ocean FW budget has not been analyzed for the new generation of climate models participating in CMIP5, despite the changes that can be expected compared to CMIP3 due to the improvements to the simulation of the Arctic sea ice and the additional open passages in the Canadian Arctic Archipelago. The use of the large CESM ensemble provides an unique opportunity to assess the role of internal variability in terms of the Arctic FW budget, and comparisons to across-model scatter from CMIP5 will allow insight on the sources of uncertainty in future projections. Furthermore, the use of FW tracers in the CESM will allow a more detailed comparison with a new set of observations and will enable analysis of the dynamics that lead to the observed interannual variability of FW from different sources in two key regions in the Arctic.