Collaborative Research: A Teleconnection between the Tropical Madden-Julian Oscillation and Arctic Sudden Stratospheric Warming Events in Warm Climates

北半球平流层的冬季风形成了一个涡旋，在北极上空的一个寒冷的低压环流周围循环。偶尔，也许十年六次，涡旋会经历一次被称为平流层突然变暖(SSW)的重大破坏，在这种情况下，北极平流层在短短几天内变暖数十摄氏度。SSW通常伴随着冷空气爆发和其他形式的恶劣天气，因此它们既具有实用价值，也具有科学价值。对SSW的经典研究证实，涡旋的破裂是由行星级的波向上并向北传播到极地平流层造成的。这些波可以以不同的方式产生，PI和其他人之前的工作发现，一些SSW可以与热带马登-朱利安涛动(MJO)有关。MJO是在赤道印度洋上空形成的云层和对流降雨的广泛包层，向东缓慢传播到中太平洋。众所周知，由MJO产生的行星波会影响中高纬度地区的天气，但它们对SSW的影响直到最近才受到广泛关注。鉴于最近的研究表明，当热带海洋表面温度(SSTs)升高时，MJO的活动增加，MJO-SSW的联系特别令人感兴趣。MJO活动的增加意味着SSW频率更高，但也必须考虑其他因素，如气候变暖时急流的变化。本项目在不同复杂程度的模式层次中研究MJO与SSW的联系。这项研究是由一个专门的模式配置实现的，它能够模拟MJO和SSW。众所周知，在当前的天气和气候模型中，MJO很难捕捉到。该模型使用超参数化(SP)，这是一种由PI之一首创的技术，在该技术中，云解析模型被嵌入到全球模型的每个网格列中(见AGS-0425247)。将SP技术应用于共同体大气模型(CAM，共同体地球系统模型的大气分量模型)中，这里使用了增强的垂直分辨率来捕捉平流层动力学。由于SSW对北半球地面天气的影响，这项工作产生了更广泛的影响。热带海温变暖增加了更强MJO事件的可能性，了解更强的事件将如何影响美国和其他国家的天气制度具有实际意义。此外，MJO的缓慢传播为与SSW相关的极端天气的大范围预报带来了希望，因此MJO-SSW联系的研究对业务天气预报具有重要意义。该项目通过暑期实习产生了更广泛的教育影响，为接受过蟒蛇编程和大气数据分析培训的本科生和当地高中生提供支持。该奖项还为两名研究生提供支持和培训，从而为这一研究领域的未来劳动力提供支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The wintertime winds of the Northern Hemisphere stratosphere form a vortex circulating around a cold low pressure cell over the Arctic. Occasionally, perhaps six time in a decade, the vortex experiences a major disruption known as a stratospheric sudden warming (SSW), in which the Arctic stratosphere warms by tens of degrees celsius in just a few days. SSWs are often followed by cold air outbreaks and other forms of severe weather, thus they are of practical as well as scientific interest. Classical studies of SSWs established that the breakdown of the vortex is caused by planetary-scale waves propagating upward and northward into the polar stratosphere. These waves can originate in various ways, and previous work by the PIs and others finds that some SSWs can be linked to the tropical Madden-Julian Oscillation (MJO). The MJO is a broad envelope of cloudiness and convective rainfall that forms over the equatorial Indian Ocean and propagates slowly eastward as far as the central Pacific. Planetary waves generated by the MJO are known to affect weather in middle and high latitudes but their effect on SSWs has not received much attention until recently. The MJO-SSW connection is of particular interest given recent studies suggesting that MJO activity increases when tropical sea surface temperatures (SSTs) increase. The increase in MJO activity suggests greater SSW frequency, but other factors such as changes in the jet streams in a warming climate must also be considered.This project examines the MJO-SSW connection in a hierarchy of models of varying degrees of complexity. The research is enabled by a specialized model configuration which is capable of simulating both the MJO, which is notoriously difficult to capture in current weather and climate models, and SSWs. The model uses superparameterization (SP), a technique pioneered by one of the PIs in which cloud resolving models are embedded in every grid column of a global model (see AGS-0425247). The SP technique is applied in the Community Atmosphere Model (CAM, the atmospheric component model of the Community Earth System Model), used here with enhanced vertical resolution to capture stratospheric dynamics. The work has broader impacts due to the effects of SSWs on surface weather in the Northern Hemisphere. The warming of tropical SSTs raises the prospect of stronger MJO events, and it is of practical interest to understand how stronger events will affect weather regimes over the US and other countries. Moreover, the slow propagation of the MJO offers some hope for extended-range prediction of extreme weather linked to SSWs, thus research on the MJO-SSW connection has implications for operational weather forecasting. The project has educational broader impacts through summer internships supporting undergraduates and local high school students, who are trained in python programming and atmospheric data analysis. The award also provides support and training to two graduate students, thereby providing for the future workforce in this research area.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.