Collaborative Research: Arctic climate sensitivity to freshwater forcing: Improving model-data comparisons of the 8.2 ka event**

ABSTRACTMorrillOPP-0713951Otto-BliesnerOPP-0713971Intellectual的优点：首席研究人员将整合气候模型和古气候记录，以更好地了解北极气候系统对北大西洋变暖的敏感性。对大西洋经向翻转环流(MOC)未来变化的模式预测具有很大的价值。因为MOC在决定环北大西洋的气候方面起着核心作用，所以我们必须知道这些模式中的哪个(如果有的话)具有预测MOC反应的技能。对模型的一个有用的测试是模拟过去MOC的变化，在强迫和响应相当熟悉的时候。一个时间段，即8.2ka事件，已被几个建模小组选为测试案例。在环北大西洋古气候记录中，这一事件被认为是一个突如其来的冷期。它的假设原因是冰川湖阿加西湖流入哈德逊湾，到目前为止完成的模拟主要集中在这种强迫上。然而，还有其他的同龄强迫，以及用来模拟淡水通量的方法中的不确定性，还有待审查。PIS将完成三组模拟，以量化这些额外强迫和强迫方法的重要性。这些模拟将使用NCAR社区气候系统模型第3版(CCSM3)完成。第一组模拟的目标将是比较不同的淡水添加方法，或称“冲洗”。目前还没有公认的冲洗方法，他们的实验将允许他们为通用方法提出建议。第二组模拟将系统地研究模型对除冰川湖泊排水之外发生的其他三种淡水通量的响应。据推测，这些来源中的每一个在产生海洋和气候反应方面都发挥了特殊的作用。在最后一组模拟中，他们将考虑额外大气作用力的影响。这些额外的强迫以前没有在模型实验中被考虑，但可能对气候反应起到了作用。这项研究将是以现实的方式将所有重要的作用力纳入8.2ka事件模拟的第一步。这对于理解北极气候敏感性以及耦合气候模型准确反映这种敏感性的能力至关重要。更广泛的影响：大西洋MOC的变化可能会在环北大西洋及更远的地区产生大规模和快速的气候扰动。这项拟议的研究将通过评估我们预测未来与北大西洋淡水增加相关的快速变化的能力来造福社会。首席调查人员将参与与国家科学基金会支持的其他研究人员以及世界各地参与古海星模型比对项目的科学家的协同合作。这项研究的成果将是他们产生的模型输出，并与古气候模拟国际比较项目一起存档。模型数据还将通过NCAR CCSM古气候工作组向科学界提供。这项研究将通过将女科学家和一名学生纳入NCAR的SOARS项目，增加未被充分代表的群体的参与。

ABSTRACTMorrillOPP-0713951Otto-BliesnerOPP-0713971Intellectual merit: The Principal Investigators will integrate climate modeling and paleoclimate records to better understand the sensitivity of the Arctic climate system to freshening of the North Atlantic. Model projections of future changes in the Atlantic meridional overturning circulation (MOC) have a large spread of values. Because the MOC plays a central role in determining the climate of the circum-North Atlantic, it is essential that we know which, if any, of these models has skill in predicting the response of the MOC. One useful test of the models is to simulate past changes in the MOC, at times when the forcing and response are reasonably well known. One time period, the 8.2 ka event, has been selected as a test case by several modeling groups. This event is observed as an abrupt cool period in circum-North Atlantic paleoclimate records. Its hypothesized cause is the drainage of glacial Lake Agassiz into Hudson Bay, and simulations completed to-date have focused mainly on this forcing. There are, however, other coeval forcings, as well as uncertainties in the methods used to model freshwater fluxes, that have yet to be examined. The PIs will complete three sets of simulations to quantify the importance of these additional forcings and the forcing methodology. These simulations will be completed using the NCAR Community Climate System Model Version 3 (CCSM3). The goal of the first set of simulations will be to compare different methods of freshwater addition, or "hosing." There is no accepted method of hosing and their experiments will allow them to make recommendations for a common methodology. The second set of simulations will systematically investigate the model response to three other freshwater fluxes that occurred in addition to the glacial lake drainage. It is hypothesized that each of these sources played a particular role in generating the ocean and climate response. In the last set of simulations, they will consider the effects of additional atmospheric forcings. These additional forcings have not been previously considered in model experiments, but could have contributed to the climate response. The research will be a first step toward incorporating all significant forcings in a realistic manner in simulations of the 8.2 ka event. This is essential for understanding Arctic climate sensitivity and the ability of coupled climate models to accurately reflect this sensitivity. Broader impacts: Changes in the Atlantic MOC can produce large and rapid climaticperturbations in the circum-North Atlantic and beyond. The proposed research willbenefit society by evaluating our ability to predict future rapid changes associated with freshwater increases in the North Atlantic. The Principal Investigators will participate in synergistic collaborations with other researchers supported by NSF and with scientists worldwide participating in the Paleohosing Model Intercomparison Project. A deliverable of this research will be the model output they generate, archived with the Paleoclimate Modeling Intercomparison Project. The model data will also be available to thescientific community through the NCAR CCSM Paleoclimate Working Group. Thresearch will increase the participation of under-represented groups by including women scientist and a student in the SOARS program at NCAR.