Quantifying Sources and Sinks of Rossby Wave Activity in the Atmosphere

量化大气中罗斯贝波活动的源和汇

• 批准号: 2154523
• 负责人: Noboru Nakamura
• 金额: $ 97.43万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2154523&HistoricalAwards=false
• 关键词: Quantifying; Sources; Sinks; Rossby; Wave

It is useful to think of the atmospheric circulation above the middle latitudes as a progression of waves, with alternating northward and southward air flow, superimposed on an eastward-flowing mean jet stream. The theory based on this wave-mean flow framework has been successful in explaining many aspects of the general circulation including the evolution of frontal weather systems and the effect of mountains on the upper-tropospheric flow. The Prpincipal Investigator (PI) has contributed to this theory by developing a measure of waviness which captures a trade-off in which wave activity increases at the expense of mean jet speed and vice versa, a consequence of the fluid analog of angular momentum conservation known as Kelvin's circulation theorem. The measure is called Finite Amplitude Wave Activity (FAWA), where finite amplitude refers to the fact that the measure can be used even when the waves distort the flow enough to create large circulation features which break off from the prevailing flow. FAWA represents the bulk wave activity around a latitude circle, and the PI has developed a related quantity called Local Wave Activity (LWA) to express waviness at each longitude along a latitude circle. Previous work by the PI's team has used the FAWA/LWA framework to explain the breakdown of the polar vortex during Sudden Stratospheric Warmings (SSWs) and the formation of blocking anticyclones (see AGS-1909522).The application of FAWA and LWA to problems like SSWs and blocking relies on their ability to capture interactions between waves and the eastward mean flow, which can be understood without knowing how the waves are generated or what eventually happens to them. But the generation and dissipation of wave activity are also represented in the evolution equations for FAWA and LWA, and the equations can be used to study wave sources and sinks and their role in atmospheric circulation. For example the dissipation of wave activity through diffusive mixing matters for the strength of the low-latitude meridional overturning cells (the Hadley cells), thus analysis of the sink term could offer insights into the expansion of the cells and the associated aridification seen in climate change simulations. Analysis of sources and sinks is promising but also challenging due to the need for intricate calculations involving small spatial scales and quantities which are hard to observe. Work under this award takes up the challenge, using a variety of techniques applied to idealized models, archived climate model output, and observational datasets (the ERA5 reanalysis in particular). Topics to be addressed through source/sink analysis include the seasonal cycle of wave activity, the role of the atmospheric boundary layer in generating and damping wave activity, and the generation of wave activity by condensational heating in convective clouds.The work has societal value due to the connection between upper-tropospheric waviness and surface weather, for instance blocking events are associated with extreme precipitation and SSWs can lead to severe cold air outbreaks. The software used to generate FAWA, LWA, and source/sink terms will be made openly available to the public via github, along with documentation on their use. Education and outreach are conducted through a biennial summer school and a local community science center. In addition, the project supports two graduate students and a postdoctoral fellow, thereby fostering the next generation of scientists 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.

把中纬度以上的大气环流看作是波的发展是有用的，它有交替的南北气流，叠加在一个向东流动的平均急流上。 基于这种波平均流框架的理论已经成功地解释了大气环流的许多方面，包括锋面天气系统的演变和山脉对对流层上层流动的影响。 PrpinUNRInvestigator（PI）通过开发一种测量波度的方法对这一理论做出了贡献，该方法捕获了一种权衡，其中波活动以平均射流速度为代价增加，反之亦然，这是角动量守恒的流体模拟的结果，称为开尔文环流定理。该措施被称为有限振幅波活动（FAWA），其中有限振幅是指即使当波浪足以扭曲流动以产生从主流中脱离的大环流特征时，也可以使用该措施。 FAWA表示围绕纬度圈的体波活动，PI开发了一个相关的量，称为局域波活动（LWA），以表示沿沿着纬度圈的每个经度处的波度。 PI团队先前的工作使用FAWA/LWA框架来解释平流层突然变暖（SSW）期间极涡的破裂和阻塞反气旋的形成（参见AGS-1909522）。FAWA和LWA对SSW和阻塞等问题的应用依赖于它们捕获波浪与向东平均流之间相互作用的能力，这是可以理解的，而不需要知道波是如何产生的，或者最终会发生什么。但波动的产生和消散也反映在FAWA和LWA的演化方程中，这些方程可以用来研究波动的源和汇及其在大气环流中的作用。 例如，波活动通过扩散混合的耗散关系到低纬度纬纬向翻转环流（Hadley环流）的强度，因此对汇项的分析可以提供对气候变化模拟中看到的环流扩张和相关干旱化的见解。 分析源和汇是有前途的，但也具有挑战性，因为需要复杂的计算，涉及小的空间尺度和数量，难以观察。 该奖项下的工作接受了挑战，使用各种技术应用于理想化模型，存档的气候模型输出和观测数据集（特别是ERA 5再分析）。 通过源/汇分析解决的主题包括波活动的季节性循环，大气边界层在产生和衰减波活动中的作用，以及对流云中凝结加热产生波活动。由于对流层上层波度和地面天气之间的联系，这项工作具有社会价值，例如阻塞事件与极端降水有关，SSW可导致严重的冷空气爆发。 用于生成FAWA、LWA和源/汇术语的软件将通过github向公众开放，沿着提供有关其使用的文档。 通过两年一度的暑期学校和当地社区科学中心开展教育和外联活动。此外，该项目还资助了两名研究生和一名博士后研究员，从而培养了该研究领域的下一代科学家。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。