Collaborative Research: Dynamical Mechanisms for Midlatitude-Arctic Interactions and Associated Weather Extremes in a Warming Climate

冬季持续的天气系统会导致寒流、暴雨或降雪。这些极端天气与中纬度急流的位置和强度密切相关，这些急流从西向东吹，经常向南北转移。随着地球气候变暖，急流受到北极表面快速变暖和热带对流层上层变暖加剧的拉锯战的影响。研究人员将研究中纬度-北极相互作用和相关极端天气的几个相互关联的动力机制。第一个主题是平流层中的行星波与寒冷事件风险之间的联系。这项任务将检验平流层极地涡旋中的极端波浪事件作为北美寒冷事件季节性可预测性来源的假设。平流层和地表温度之间的这种联系将在观测和气候模式中加以分析。其次，调查人员将检验一个假设，即在北极快速变暖的情况下，较弱的急流将导致中纬度地区出现更频繁的极端天气。这项任务将进行理想化的数值模拟，以检验射流速度或射流结构对射流南北向移的影响，从而试图调和关于中纬度环流波浪度随气候变暖变化的不同观点。第三项任务是关于大气河流，即与中纬度气旋有关的狭窄的强烈水汽输送。大气河流主导着中高纬度地区向极地方向的水汽通量，对北极变暖有贡献。强烈的水汽输送可以受到风速或温度的影响，这两个因素将在水蒸气和云示踪剂的大气输送模式中进行研究。中纬度极端天气具有深远的社会经济影响。来自极端平流层事件的预测技能可以改善北美冬季寒流的分季节预报，对能源消耗和运输具有重要意义。更好地了解气候变暖中的极端寒冷事件可以促进科学界与公众之间更好地交流全球变暖科学。改进了对中纬度气旋向北极输送强烈水汽的预测，有助于更好地适应不断变化的北极。除了支持宾夕法尼亚州立大学的一名早期职业科学家外，该提案还将培训加州大学洛杉矶分校的两名研究生研究人员分析观测和气候模型。加州大学洛杉矶分校的几名本科生将接受气候数据统计分析方面的培训，特别是针对STEM专业和代表性不足的少数族裔。本研究中开发的理想模型将在GitHub网站上提供，并附带示例python脚本。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Persistent weather systems in winter cause cold spells, heavy rainfall, or snow. These weather extremes are closely related to the location and intensity of midlatitude jet streams, which blow from west to east and often shift to the north and south. As Earth’s climate gets warmer, the jet streams are affected by the tug-of-war between the rapid surface warming over the Arctic and the enhanced upper-tropospheric warming in the tropics. The investigators will examine several interrelated dynamical mechanisms for midlatitude-Arctic interactions and the associated weather extremes. The first theme is the linkage between the planetary waves in the stratosphere and the risk of cold events. This task will test the hypothesis that extreme wave events in the stratospheric polar vortex serve as a source of intraseasonal predictability for cold events over North America. This linkage between the stratosphere and surface temperature will be analyzed in observations and climate models. Secondly, the investigators will examine a hypothesis that a weaker jet stream under rapid Arctic warming would lead to more frequent weather extremes in mid-latitudes. This task will perform idealized numerical simulations to examine the effect of jet speed or jet structure on the north and south shifts of a jet and thus attempt to reconcile different views on the changes in midlatitude circulation waviness in response to climate warming. The third task is on atmospheric rivers, the narrow intense moisture transport associated with midlatitude cyclones. Atmospheric rivers dominate the poleward moisture flux in the middle and high latitudes, which contribute to Arctic warming. Intense moisture transport can be influenced by either wind speed or temperature, and the two factors will be studied in an atmospheric transport model of water vapor and cloud tracers.Midlatitude weather extremes have profound socioeconomic impacts. Predictive skills from extreme stratospheric events could improve the sub-seasonal forecast of winter cold spells over North America, with important implications for energy consumption and transportation. A better understanding of extreme cold events in a warming climate can foster better communications of global warming science between the scientific community and the public. Improved predictions of the intense moisture transport by midlatitude cyclones into the Arctic help better adapt to the changing Arctic. Besides supporting an early career scientist at Penn State University, the proposal will train two graduate student researchers at UCLA in the analysis of observations and climate models. Several UCLA undergraduates will be trained in statistical analysis of climate data, particularly for STEM majors and underrepresented minorities. The idealized models developed in this study will be made available on a GitHub website with sample python scripts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.