Extratropical Persistent Anomalies on a Warmer Earth: Connections to Extratropical Storms and Storm Tracks

温暖地球上的温带持续异常：与温带风暴和风暴路径的联系

• 批准号: 1560844
• 负责人: Walter Robinson
• 金额: $ 97.19万
• 依托单位: North Carolina State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1560844&HistoricalAwards=false
• 关键词: Extratropical; Persistent; Anomalies; Warmer; Earth

This is a study of persistent anomalies (PAs) in atmospheric circulation, defined as unusual states of the atmospheric flow that remain approximately fixed over periods longer than a few days. PAs addressed here occur in middle latitudes when the normal eastward progression of weather systems over a given location is disrupted. They are generally associated with splitting or meridional shifting of jet streams and are loosely synonymous with atmospheric blocking, although blocking has a more restrictive definition. Interest in PAs comes largely from their association with high-impact weather events including cold air outbreaks, droughts, pluvials, and heat waves. The project seeks to understand the fundamental dynamics which determine the frequency, intensity, and duration of persistent anomalies (PAs), as well as the changes in PA behavior that are likely to occur as a result of warming due to greenhouse gas increases.PAs are broader in spatial scale than the weather fronts and cyclones that are collectively referred to as synoptic systems. Studies of blocking show that synoptic systems play a large role in the onset and maintenance of blocks, a finding that holds true for PAs as well. The PIs hypothesize that the initiation and maintenance of PAs depends on smaller-scale processes that occur inside the synoptic systems, including the organization of rain-bearing clouds (where condensational heating occurs) into mesoscale features (rain bands and squall lines, for example). The hypothesis is motivated in part by studies showing that global weather and climate models with higher resolution do a better job in simulating blocks, despite the large size of blocks compared to grid spacing even in low resolution models. The PIs propose that higher resolution is better because it allows a more accurate representation of the much smaller mesoscale features where the condensational heating takes place. Better representation of condensational heating leads to more vigorous systems, which can more effectively move low vorticity air across the jet stream from the tropics to high latitudes as required for PA formation. One implication of this hypothesis is that models or climate states which are more conducive to high intensity synoptic systems will produce more strong PAs. This argument suggests that PAs could become stronger or more prominent as climate warms, as the greater moisture content of warmer air allows for more intense rainfall and condensational heating.The project examines PAs in present-day climate by identifying a set of cases and performing "hindcast" simulations of those cases using a global atmospheric model (the Weather Research and Forecasting model, or the Model for Prediction Across Scales if it becomes available). Model configurations which produce the best simulations of these cases will be identified, and a number of diagnostics will be performed to identify the key ingredients which lead to PA initiation and persistence. Additional experiments are performed using a technique in which the initial atmospheric state for the simulation is modified to remove particular synoptic features, in order to assess the role of these features in PA formation. The impact of climate change on PAs is studied by repeating the hindcasts but with the background state modified to approximate the effects of greenhouse warming as simulated by climate models. Long model integrations are used to consider PA behavior in a statistical sense, and simple single-layer models are used to further examine the basic dynamics of PAs.The behavior of PAs is a topic of practical as well as scientific interest, given the close association of PAs with high-impact weather events that affect human activities. The work addresses questions which are directly relevant to improving the ability of weather models to forecast PA-related extreme weather, and the ability of climate models to anticipate future changes in PA behavior. In addition, the project provides undergraduate research opportunities through two new courses emphasizing collaborative research, one on data analysis and the other on numerical simulations. An undergraduate internship is also supported in each summer of the project, and the position is advertised at minority-serving institutions. In addition, the project will employ and train two graduate students and a postdoctoral fellow, thereby providing future workforce development in this area of research.

这是一项关于大气环流持续异常（PA）的研究，定义为在几天以上的时间内保持近似固定的大气流动的不寻常状态。 这里讨论的PA发生在中纬度地区，当给定位置的天气系统的正常东进被破坏时。它们通常与急流的分裂或纬向移动有关，与大气阻塞大致同义，尽管阻塞的定义更具限制性。 对PA的兴趣主要来自于它们与高影响天气事件的关联，包括冷空气爆发，干旱，暴雨和热浪。 该项目旨在了解决定持续异常（PAs）的频率，强度和持续时间的基本动力学，以及由于温室气体增加而导致的变暖可能导致的PA行为的变化。PAs在空间尺度上比统称为天气系统的天气锋和气旋更广泛。 阻塞的研究表明，天气系统在阻塞的发生和维持中起着很大的作用，这一发现也适用于PA。 PI假设PA的启动和维持取决于天气系统内部发生的小尺度过程，包括将降雨云（发生凝结加热的地方）组织成中尺度特征（例如雨带和飑线）。 这一假设的部分动机是研究表明，具有较高分辨率的全球天气和气候模式在模拟块方面做得更好，尽管即使在低分辨率模式中，与网格间距相比，块的大小也很大。PI建议分辨率越高越好，因为它可以更准确地表示发生冷凝加热的较小中尺度特征。 更好地代表冷凝加热导致更有力的系统，它可以更有效地移动低涡度空气穿过急流从热带到高纬度地区所需的PA形成。 这一假说的一个含义是，模式或气候状态，更有利于高强度的天气系统将产生更强的PA。 这一论点表明，随着气候变暖，PA可能会变得更强或更突出，因为温暖空气的水分含量增加，降雨和凝结加热会更强烈。该项目通过确定一组案例并使用全球大气模型对这些案例进行“后报”模拟来研究当今气候中的PA（天气研究和预报模型，或跨尺度预测模型（如果可用））。 将确定产生这些情况下的最佳模拟的模型配置，并将进行一些诊断，以确定导致PA启动和持续的关键成分。使用一种技术，在该技术中，初始大气状态的模拟被修改，以消除特定的天气特征，以评估这些功能在PA形成的作用进行额外的实验。 气候变化对保护区的影响是通过重复后报来研究的，但是背景状态被修改为近似于气候模式模拟的温室效应。 长模型积分被用来考虑PA的行为在统计意义上，和简单的单层模型被用来进一步研究的基本动力学的PAs.The行为的PAs是一个主题的实际和科学的兴趣，考虑到PA与高影响力的天气事件，影响人类活动的密切关联。 这项工作解决了与提高天气模型预测PA相关极端天气的能力以及气候模型预测PA行为未来变化的能力直接相关的问题。 此外，该项目通过两门新课程提供本科生研究机会，这两门课程强调合作研究，一门是数据分析，另一门是数值模拟。 在该项目的每个夏季，还支持本科生实习，并在为少数群体服务的机构刊登招聘广告。 此外，该项目将雇用和培训两名研究生和一名博士后研究员，从而为这一研究领域的未来劳动力发展提供支持。