Collaborative Research: NSF-BSF--Tropospheric Response to Zonal Asymmetry of the Stratospheric Polar Vortex and Its Aapplication to Subseasonal to Seasonal (S2S) Prediction

平流层是位于影响地球表面天气的云层和风暴之上的大气层。但是，尽管平流层位于天气上方，但它仍然影响着天气，特别是当冬季在极地冰盖上方形成的向东移动的涡旋在被称为平流层突然变暖(SSW)的事件中破裂时。预计对流层对SSW的反应是极冠上方更高的地面气压，更频繁地发生冷空气爆发，以及更频繁的沿海和东北风暴。因此，SSW对亚季节转季节(S2S)天气预报非常有意义，SSW影响地面天气的机制已经得到了深入的研究。该奖项下的工作旨在更好地了解SSW和其他不太极端的平流层极涡干扰对对流层环流和地面天气的影响。一个关键的问题是，一些SSW对底层对流层有很强的影响，而另一些则没有，而且表面温度异常的分布在不同的极地涡旋干扰之间可能有很大的不同。首席研究人员假设，对流层响应的差异部分是由于在极地涡旋破坏过程中发生的扭曲模式。例如，在一些SSW中，在平流层极地涡旋破裂后形成“子涡”，地表温度响应可能随子涡的位置而变化。研究涉及对观测数据集、耦合模式相互比较项目(CMIP)提供的模拟输出的分析，以及亚季节到季节性(S2S)预报和隐藏预报的集合，包括通过国家多模式集合(NMME)获得的预报和隐藏预报。数据分析工作得到了来自理想潮湿大气模式(MIMA)的模拟的补充，MIMA是一个简化的模式，能够模拟诺赫特恩半球冬季环流的真实特征，包括急流、定常波和平流层极涡。实验是通过使用人为的阻力来诱导具有特定地理扭曲的涡旋破坏，以便评估它们对地表温度的影响。鉴于平流层涡旋破坏与极端冬季天气之间的联系，这项工作具有社会和科学意义。其中一名首席调查人员开设了一个博客，作为北半球目前和预报天气模式的技术和非技术讨论的门户。该项目还为一名研究生和一名博士后助理提供支持和培训。这是一个由国家科学基金会地球科学理事会(NSF-GEO)和以色列双国科学基金会(BSF)联合资助的项目，符合NSF和BSF谅解备忘录中的语言。该协议允许由美国和以色列调查人员参与的单一合作提案提交，并由NSF进行同行审查。根据NSF功绩审查和认可NSF计划推荐的奖项的成功结果，每个机构将为与其本国相关的预算和调查人员的比例提供资金。该奖项反映了NSF的法定使命，并已通过使用基金会的知识功绩和更广泛的影响审查标准进行评估，被认为值得支持。

The stratosphere is the layer of the atmosphere that sits above the clouds and storms that affect weather at the earth's surface. But despite being above the weather the stratosphere still influences the weather, particularly when the eastward-moving vortex that forms in winter over the polar cap breaks down in events called sudden stratospheric warmings (SSWs). The expected tropospheric response to an SSW is higher surface pressure over the polar cap, more frequent occurrence of cold air outbreaks, and and more frequent coastal Nor'easter storms. SSWs are thus of great interest for subseasonal to seasonal (S2S) weather prediction, and the mechanisms through which SSWs influence surface weather have been intensively studied. Work under this award seeks to improve understanding of the effects of SSWs and other less extreme stratospheric polar vortex disruptions on tropospheric circulation and surface weather. A key issue is that some SSWs have a strong effect on the underlying troposphere while others do not, and the distribution of surface temperature anomalies can be quite different from one polar vortex disruption to another. The Principal Investigators hypothesize that differences in the tropospheric response are due in part to the pattern of distortions that occur over the course of a polar vortex disruption. For instance in some SSWs a "daughter" vortex forms after the stratospheric polar vortex breaks down, and the surface temperature response could vary depending on the location of the daughter vortex.The research involves analysis of observational datasets, output from simulations available through the Coupled Model Intercomparison Project (CMIP), and ensembles of subseasonal to seasonal (S2S) forecasts and hidcasts including those available through the National Multi-Model Ensemble (NMME). The data analysis effort is complemented by simulations from the Model of an Idealized Moist Atmosphere (MIMA), a simplified model capable of simulating realistic features of the Norhtern Hemisphere winter circulation including jet streams, stationary waves, and the stratospheric polar vortex. Experiments are conducted by using an artificial drag force to induce vortex disruptions with specific geographical distortions so that their effects on surface temperature can be assessed.The work is of societal as well as scientific interest given the connection between stratospheric vortex disruptions and extreme winter weather. One of the Principal Investigators maintains a blog that serves as a portal for technical and non-technical discussion of present and forecasted weather patterns for the Northern Hemisphere. The project also provides support and training for a graduate student and a postdoctoral associate.This is a project jointly funded by the National Science Foundation's Directorate of Geosciences (NSF-GEO) and the Israel Binational Science Foundation (BSF) in accord with the language in the Memorandum of Understanding between the NSF and the BSF. This Agreement allows a single collaborative proposal, involving US and Israeli investigators, to be submitted and peer-reviewed by NSF. Upon successful results of the NSF merit review and recommendation by the cognizant NSF Program of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.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.