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

在未来几十年里，北极淡水系统可能会发生相当大的变化，对海洋环流、气候和生态系统产生下游影响。 理解和预测这些影响的能力反过来将对渔业、能源分配和再保险行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气候变化中的重要性的认识也很有限。 该项目旨在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。 该项目将通过在其职业生涯的形成期向年轻的职业早期女性PI提供支持并支持研究生的培训，为STEM劳动力发展做出贡献。 PI将利用她与国家大气研究中心的联系，将项目成果纳入其面向公众的外展展览中。 研究结果也将被纳入公开讲座和大学讲座。本项目将研究以下主要科学问题：1。气候模型是否显示了21世纪及以后北冰洋FW变化的一致性？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.在气候模拟中，北极FW收支的不同项的内部变率的作用有多大？这对不同时间尺度的未来预测的不确定性有何影响？为了捕捉内部变化的幅度，一个系综需要多大？3.弗拉姆海峡和开关站区域的模拟FW分量与过去十年的观测结果一致程度如何？导致不同来源的FW发生变化的动力是什么？为了解决这些问题，首先北冰洋淡水（FW）预算的耦合模式相互比较项目第5阶段（CMIP 5）模拟套件的20和21世纪世纪将进行评估，然后由内部变化的北极FW预算条款的作用分析在一个大的合奏模拟从社区地球系统模型（CESM）。最后，来自不同来源的FW的贡献在弗拉姆海峡和北极开关站地区的CESM将与观测使用新的模拟FW示踪剂进行比较，北冰洋动力学导致FW的变化从不同的来源将进行调查。尽管由于北极海冰模拟的改进和加拿大北极群岛的额外开放通道，与CMIP 3相比可以预期会发生变化，但尚未对参与CMIP 5的新一代气候模式进行北冰洋FW预算分析。大型CESM集合的使用提供了一个独特的机会，以评估北极FW预算方面的内部变化的作用，并与CMIP 5的跨模型散射进行比较，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，并将能够分析导致在北极两个关键区域观察到的来自不同来源的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.