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.

这是对大气循环中持续异常（PA）的研究，该研究被定义为大气流动的异常状态，在大约时间内固定的时间长于几天。 当天气系统在给定位置的正常向东进展时，此处解决的PA发生在中纬度中。它们通常与喷气流的分裂或子午转移有关，并且与大气阻塞的代名词宽松地同义，尽管阻塞的定义更具限制性。 对PAS的兴趣主要来自与高影响的天气事件的关联，包括冷空气暴发，干旱，pluvials和热浪。 该项目试图了解决定持续异常的频率，强度和持续时间（PAS）的基本动力学，以及PA行为的变化可能是由于温室气体增加而导致的，因为温室气体增加了。 封锁的研究表明，概要系统在块的发作和维护中起着很大的作用，这一发现也适用于PAS。 PI假设PA的启动和维护取决于概要系统内发生的较小规模的过程，包括将雨云（例如，在降雨带来的雨水和雨带和quall云线）中组织（例如，降温加热发生）。 该假设是通过研究表明，尽管与网格间距相比，甚至在低分辨率模型中，但分辨率较高的全球天气和气候模型在模拟块方面的效果更好。 PI提出，更高分辨率更好，因为它允许更准确地表示发生凝结加热的较小的中尺度特征。 更好地代表冷凝的加热会导致更有活力的系统，这可以更有效地将低涡度空气从热带地区转移到PA形成所需的高纬度地区。 该假设的一个含义是，更有利于高强度概要系统的模型或气候状态将产生更强大的PA。 这一论点表明，随着气候温暖的变化，PAS可能会变得更强大或更突出，因为较高的温暖空气的水分含量可以进行更强烈的降雨和凝结供暖。该项目通过确定一组案例并执行一系列案例并使用这些案例进行这些案例模拟的“天气研究”模型（如果天气研究和预测模型）进行预测，从而在当今的气候下检查PAS。 将确定产生最佳模拟的模型配置，并将执行许多诊断，以识别导致PA启动和持久性的关键成分。使用一种技术进行其他实验，在该技术中，对模拟的初始大气状态进行了修改以消除特定的概要特征，以评估这些特征在PA形成中的作用。 通过重复后广播来研究气候变化对PAS的影响，但背景状态修改以近似通过气候模型模拟的温室变暖的影响。 长期模型集成用于从统计意义上考虑PA行为，而简单的单层模型用于进一步检查PAS的基本动力。鉴于PAS与影响人类活动的高损坏的天气事件的密切关联，PAS的行为是实用的和科学兴趣的话题。 这些工作解决了与提高天气模型预测与PA相关的极端天气的能力以及气候模型预测未来PA行为变化的能力直接相关的问题。 此外，该项目通过两个新课程强调协作研究，一个关于数据分析，另一个关于数值模拟的新课程。 该项目的每个夏天还支持本科实习，并且该职位在少数派服务机构中做广告。 此外，该项目将聘请并培训两名研究生和一名博士后研究员，从而在这一研究领域提供未来的劳动力发展。