Improved Understanding of Changes in Convective Available Potential Energy and Links to the Large-scale Circulation

更好地了解对流可用势能的变化以及与大规模环流的联系

• 批准号: 1749986
• 负责人: Paul O'Gorman
• 金额: $ 41.21万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-03-01 至 2022-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1749986&HistoricalAwards=false
• 关键词: Improved; Understanding; Changes; Convective; Available

The build-up of a thunderstorm, from scattered popcorn clouds to a dark towering storm cloud, is a common sight on a summer afternoon. The vigorous growth of such clouds is fueled by the convective available potential energy (CAPE) of the atmosphere. Formally CAPE is the amount of work that would be done by the buoyancy force on a saturated plume of air rising through the portion of the atmosphere in which it is lighter than the surrounding air, assuming that no ambient air mixes into the rising plume. Weather forecasters routinely calculate CAPE from atmospheric temperature soundings and use it to predict the likelihood of severe convective storms.Computer simulations of greenhouse-gas induced climate change commonly show large increases of CAPE with global mean temperature, a result which has raised concerns that thunderstorms may become more common or intense as a consequence of climate change. But the reasons why CAPE should increase with global temperature are not clear, and the lack of a theory for the dependence of CAPE on temperature limits confidence in model results.Under previous funding the PI's group developed a simple model which explains the dependence of CAPE on temperature. But the theory assumes that the atmosphere is in a state of radiative-convective equilibrium, a state which approximates the condition of the atmosphere over warm tropical oceans. The theory is compelling as a starting point but cannot be directly applied to understand CAPE change over land or at higher latitudes. Work under this award thus seeks a more general understanding of the relationship between CAPE and global climate, including the effects of large-scale atmospheric circulation. The research is conducted through examination of climate model simulations produced for the Coupled Model Intercomparison Project, combined with experiments using a cloud resolving model on a limited domain to test hypotheses. The role of atmospheric circulation is assessed through calculation and analysis of moist mean available potential energy (MAPE), the maximum amount of kinetic energy that can be reversibly produced from the mean state of the atmosphere by transforming to a lower energy reference state. The MAPE analysis seeks to relate the mean state of the atmosphere in middle and high latitudes to its potential to generate CAPE through large-scale circulations. The impact of land surface conditions on CAPE is another focus of the research, as the strong diurnal cycle of temperature and moisture plays a key role in the development of convection over land. Further work considers the impact of changes in CAPE on the Walker circulation, a large-scale overturning circulation between the western and eastern Pacific.The work has societal as well as scientific value given the damaging effects of convective storms, including hail, lightning, tornados, and flash floods, along with indications that their intensity or frequency of occurrence may increase due to climate change. Results with practical implications are shared with interested parties through workshops and other venues, and research results are incorporated into classroom teaching and other educational activities. In addition, the project provides support and training to a graduate student, thereby providing for the future work force 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.

雷暴的形成，从分散的爆米花云到黑暗高耸的风暴云，是夏日午后的常见景象。这种云的蓬勃生长是由大气对流可用势能（CAPE）推动的。 CAPE 的正式形式是假设没有环境空气与上升的羽流混合，则浮力对通过比周围空气轻的大气部分上升的饱和空气羽流所做的功。 天气预报员定期根据大气温度探测计算 CAPE，并用它来预测发生强对流风暴的可能性。对温室气体引起的气候变化的计算机模拟通常显示 CAPE 随全球平均温度大幅增加，这一结果引起了人们对雷暴可能会出现的担忧。由于气候变化而变得更加普遍或严重。 但 CAPE 应随全球温度而增加的原因尚不清楚，并且缺乏 CAPE 对温度依赖性的理论限制了模型结果的可信度。在先前的资助下，PI 小组开发了一个简单的模型，该模型解释了 CAPE 对温度的依赖性温度。 但该理论假设大气处于辐射对流平衡状态，这种状态近似于温暖热带海洋上空的大气状况。 该理论作为一个起点很引人注目，但不能直接应用于理解陆地或高纬度地区的 CAPE 变化。 因此，该奖项的工作旨在更全面地了解 CAPE 与全球气候之间的关系，包括大规模大气环流的影响。 该研究是通过检查为耦合模型比较项目生成的气候模型模拟，并结合在有限域上使用云解析模型来检验假设的实验来进行的。 大气环流的作用是通过计算和分析潮湿平均可用势能（MAPE）来评估的，MAPE是大气平均状态通过转变为较低能量参考状态可逆地产生的最大动能。 MAPE 分析旨在将中高纬度地区的大气平均状态与其通过大规模环流产生 CAPE 的潜力联系起来。 地表条件对CAPE的影响是研究的另一个重点，因为温度和湿度的强烈昼夜循环在陆地对流的发展中起着关键作用。进一步的工作考虑了 CAPE 变化对沃克环流的影响，沃克环流是西太平洋和东太平洋之间的大规模翻转环流。鉴于对流风暴（包括冰雹、闪电、龙卷风）的破坏性影响，这项工作具有社会和科学价值和山洪暴发，并有迹象表明其发生强度或频率可能因气候变化而增加。具有实际意义的成果通过研讨会和其他场所与感兴趣的各方分享，并将研究成果纳入课堂教学和其他教育活动。 此外，该项目还为研究生提供支持和培训，从而为该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进行评估，认为值得支持标准。

项目成果

Weakening of the Extratropical Storm Tracks in Solar Geoengineering Scenarios

• DOI: 10.1029/2020gl087348
• 发表时间: 2020-06-16
• 期刊: GEOPHYSICAL RESEARCH LETTERS
• 影响因子: 5.2
• 作者: Gertler, Charles G.;O'Gorman, Paul A.;Watanabe, Shingo
• 通讯作者: Watanabe, Shingo

Changing available energy for extratropical cyclones and associated convection in Northern Hemisphere summer

• DOI: 10.1073/pnas.1812312116
• 发表时间: 2019-03-05
• 期刊: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• 影响因子: 11.1
• 作者: Gertler, Charles G.;O'Gorman, Paul A.
• 通讯作者: O'Gorman, Paul A.

Summer‐Winter Contrast in the Response of Precipitation Extremes to Climate Change Over Northern Hemisphere Land

北半球陆地极端降水对气候变化响应的夏冬对比

• DOI: 10.1029/2021gl096531
• 发表时间: 2022
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Williams, Andrew I.;O’Gorman, Paul A.
• 通讯作者: O’Gorman, Paul A.