Collaborative Research: New Pathways to Enhanced Turbulence and Mixing via Kelvin-Helmholtz Instability Tube and Knot Dynamics

合作研究：通过开尔文-亥姆霍兹不稳定管和结动力学增强湍流和混合的新途径

• 批准号: 2128444
• 负责人: Dale Lawrence
• 金额: $ 45.89万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-11-01 至 2024-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2128444&HistoricalAwards=false
• 关键词: Collaborative; Research; New; Pathways; Enhanced

The project seeks funding to investigate atmospheric turbulence generation. Shear layers in the atmosphere, where a layer slides over another, can result in instabilities that are commonly seen in thin cloud layers and resemble a series of ocean waves breaking on a beach. These instabilities, called Kelvin-Helmholtz instabilities, cause turbulence and mixing throughout the atmosphere and the oceans where shears are strong. Spacing between these “billows” can vary in the atmosphere from a few meters near the ground to 10 km or larger at altitudes as high as 100 km. Those seen in clouds usually have spacings (or wavelengths) from a few hundred meters to a km or so. The turbulence and mixing when these billows “break” influence the atmospheric structure and weather, especially near the ground, but their effects are not described well in weather prediction models. This research will explore a new type of instability causing breaking and turbulence that was recently discovered in thin clouds at very high altitudes that the research team expects to occur at all altitudes, and to significantly increase the turbulence and mixing due to these processes. If shown to occur for a wider range of conditions, this would significantly influence our ability to model the atmosphere near the ground and improve weather prediction that impacts all of us. The same instabilities occur in the oceans and are expected to also improve prediction of ocean circulations and structure when these processes are more fully understood. The project will involve a graduate student and a postdoctoral researcher experience in state-of-the-art modeling and super-computing. New observations of thin Polar Mesospheric Clouds and airglow layers at high altitudes (~80-90 km) have revealed the occurrence of a new type of instability leading to turbulence arising from mis-aligned Kelvin-Helmholtz (KH) billows accompanying variable geophysical forcing. These instabilities arise due to interactions among adjacent KH billow cores, rather than within single billows, and initial modeling of these dynamics have shown them to be much stronger, and to lead to much more intense turbulence, than occur in their absence. These dynamics arise from interactions between KH billow cores and large-scale vortex tubes that are excited where KH billows are mis-aligned or discontinuous due to initial conditions. Initial modeling employing direct numerical simulations that enable quantitative assessments of these dynamics, their stronger instabilities, and their more intense turbulence suggest that they may also cause enhanced turbulence and mixing in regions, and for conditions, in which turbulence was not previously expected. The research team believes that these enhanced KH billow dynamics are likely to be widespread and that they will allow us to update how these dynamics are modeled, enabling improved weather prediction, and of similar responses in the oceans. Because KH instabilities also play significant roles of other fields of physics, specifically magnetospheric physics and astrophysics, the benefits of this research may prove to be very broad.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.

该项目寻求资金来研究大气湍流的产生。大气中的剪切层（一层在另一层上滑动）可能会导致不稳定，这种不稳定在薄云层中很常见，类似于一系列海浪拍打海滩的情况。这些不稳定性被称为开尔文-亥姆霍兹不稳定性，会在剪切力较强的大气和海洋中引起湍流和混合。在大气中，这些“巨浪”之间的间距可能会有所不同，从接近地面的几米到高度高达 100 公里的 10 公里或更大。在云中看到的那些通常具有几百米到一公里左右的间距（或波长）。这些巨浪“破裂”时的湍流和混合会影响大气结构和天气，特别是在地面附近，但它们的影响在天气预报模型中并没有得到很好的描述。这项研究将探索一种新型的不稳定性，这种不稳定性会导致最近在极高海拔的薄云中发现的破裂和湍流，研究小组预计这种不稳定性会在所有高度发生，并显着增加由于这些过程而产生的湍流和混合。如果在更广泛的条件下发生这种情况，这将极大地影响我们对地面附近的大气进行建模的能力，并改善影响我们所有人的天气预报。同样的不稳定性也发生在海洋中，当这些过程得到更充分的了解时，预计也将改善对海洋环流和结构的预测。该项目将涉及一名研究生和一名博士后研究员，他们在最先进的建模和超级计算方面拥有丰富的经验。对高海拔（约 80-90 公里）的薄极地中层云和气辉层的新观测揭示了一种新型不稳定性的发生，这种不稳定性会导致由未对准的开尔文-亥姆霍兹（KH）巨浪伴随着可变的地球物理强迫而产生的湍流。这些不稳定性是由于相邻 KH 巨浪核心之间的相互作用而产生的，而不是单个巨浪内部的相互作用，并且这些动力学的初始建模表明，它们比没有它们时发生的情况要强大得多，并会导致更强烈的湍流。这些动力学源于 KH 巨浪核心与大型涡流管之间的相互作用，这些涡流管在 KH 巨浪由于初始条件而未对准或不连续的情况下被激发。采用直接数值模拟的初始模型能够对这些动力学、其更强的不稳定性和更强烈的湍流进行定量评估，这表明它们还可能在区域以及先前未预期会出现湍流的条件下引起增强的湍流和混合。研究小组认为，这些增强的 KH 巨浪动力学可能会广泛传播，并且它们将使我们能够更新这些动力学的建模方式，从而改进天气预报以及海洋中的类似响应。由于 KH 不稳定性在其他物理领域（特别是磁层物理和天体物理学）中也发挥着重要作用，因此这项研究的好处可能会非常广泛。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Instabilities, Dynamics, and Energetics accompanying Atmospheric Layering (IDEAL): high-resolution in situ observations and modeling in and above the nocturnal boundary layer

伴随大气分层 (IDEAL) 的不稳定性、动力学和能量学：夜间边界层内外的高分辨率原位观测和建模

• DOI: 10.5194/amt-15-4023-2022
• 发表时间: 2022
• 期刊: Atmospheric Measurement Techniques
• 影响因子: 3.8
• 作者: Doddi, Abhiram;Lawrence, Dale;Fritts, David;Wang, Ling;Lund, Thomas;Brown, William;Zajic, Dragan;Kantha, Lakshmi
• 通讯作者: Kantha, Lakshmi