Collaborative Proposal: The Role of Arctic Amplification in Modifying Mid-latitude Atmospheric Circulation and Promoting Extreme Weather Events

智力价值：最近的研究提出并证明了一种连接北极放大(AA？北极变暖加剧)，北半球中纬度地区发生极端天气事件的可能性增加，以及对推动冰层进一步减少的北极风型的反馈。这项研究将利用再分析的输出、CMIP5档案的模式模拟和实验性的CESM模式运行来扩展这项工作，以调查北极海冰和高纬度陆地积雪的持续消失如何以及为什么会导致中纬度天气模式的变化。500百帕高度的过去和预测的模式将使用自组织映射(SOM)的组合进行分析？一种基于神经网络的技术，可以将大型数据集缩减为它们的代表性模式？一个新的经圈环流指数和一个极端天气指数，以解决北极放大过去和未来全球气候变化促进有利于北半球中纬度极端天气事件的环流模式的假设。PI指数表明，由于高纬度陆地上海冰的消失和更早的积雪融化，北极表面能量收支的变化减少了经向厚度梯度，这导致了总体上较弱的高空纬向气流和较高的环流特征。他们认为，这些高层气流模式减缓了大规模大气Rossby波的东移，有利于更持续的天气条件，增加了冷空气爆发、热浪、干旱和强降水等极端天气的可能性。他们认为，推动这种变化的主要物理机制是北极加热的增强和季节性变化：在秋季/冬季，它是以海洋为基础的，与大量的海冰损失有关，而在温暖的月份，它主要是由于较早的积雪融化和土壤水分的减少而基于陆地的。由于极端天气事件，如温度和降水极端，通常是由高幅度、缓慢移动的高层环流模式引起的，因此这一分析将侧重于检测和表征这些模式，解释与之相关的天气条件，并确定可能受到影响的区域。这项研究试图将北极变化与全球气候系统的其他部分联系起来。更广泛的影响：温室气体积累导致的极端天气的变化将直接和戏剧性地影响全球数百万人，因此，社会各级决策者迫切需要更好地了解和更准确地预测未来干旱、洪水和极端温度的频率、位置和严重程度的变化。通过在知名报纸上发表文章、电台采访、天气频道采访、杂志文章和众多在线博客，前期工作已经引起了世界范围的关注。这也将是一个新的博士后的机会。PI将为NSF支持的？超越企鹅和北极熊？准备一个模块。面向K-5教师的项目。两家私人投资机构经常就气候变化相关问题进行公开和学校陈述，由于极端天气与整个社会如此相关，拟议研究的结果将在这些陈述中占据重要地位。

Intellectual Merit: recent work has suggested and demonstrated a mechanism connecting Arctic Amplification (AA ? enhanced Arctic warming) with an increased probability of extreme weather events in northern hemisphere mid-latitudes, as well as a feedback to arctic wind patterns that drive further ice loss. This study will extend this work using output from reanalyses, model simulations from the CMIP5 archive, and experimental CESM model runs to investigate how and why the ongoing loss of arctic sea ice and high-latitude terrestrial snow cover may cause mid-latitude weather patterns to change. Past and projected patterns in 500 hPa heights will be analyzed using a combination of Self-Organizing Maps (SOMs) ? a neural-network-based technique that reduces large data sets to their representative patterns ? a new meridional circulation index, and an extreme weather index to address the hypothesis that Arctic Amplification of past and future global climate change promotes circulation patterns that favor extreme weather events in middle latitudes of the northern hemisphere. The PIs suggest that changes in the energy budget of the arctic surface, because of sea-ice loss and earlier snow melt on high-latitude land, reduce meridional thickness gradients, which induce generally weaker zonal flow aloft and higher amplitude circulation features. They think these upper-level flow patterns slow the eastward progression of large-scale atmospheric Rossby waves, favoring more persistent weather conditions that increase the probability of extreme weather such as cold-air outbreaks, heat waves, droughts, and heavy precipitation. They believe the primary physical mechanism driving the change is an enhanced and seasonally varying arctic heating: in fall/winter it is ocean-based associated with substantial sea ice loss, while in warmer months it is land-based due primarily to earlier snow melt and reduced soil moisture. Higher-amplitude flow trajectories may also exacerbate sea-ice and snow-cover loss, thereby constituting a positive feedback loop.Because extreme weather events, such as temperature and precipitation extremes, are often caused by high-amplitude, slow-moving upper-level circulation patterns, this analysis will focus on detecting and characterizing these patterns, interpreting the weather conditions associated with them, and identifying regions that are likely to be affected. This study attempts to connect arctic change with the rest of the global climate system.Broader Impacts: Changes in extreme weather as a result of greenhouse gas accumulation will directly and dramatically affect millions of people across the globe, thus a better understanding and more accurate future projection of changes in the frequency, location, and severity of droughts, floods, and temperature extremes are urgently needed by decision-makers at all levels of society. Preliminary work has already attracted world-wide attention via articles in prominent newspapers, radio interviews, interviews for the Weather Channel, magazine articles, and numerous online blogs. This will also be an opportunity for a new post-doc. The PIs will prepare a module for the NSF-supported ?Beyond Penguins and Polar Bears? project for K-5 teachers. Both PIs make frequent public and school presentations on climate-change related issues, and because extreme weather is so relevant to society at large, results from the proposed study will figure prominently into these presentations.