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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

基本信息

批准号：
2128443
负责人：
David Fritts
金额：
$ 74.86万
依托单位：
GLOBAL ATMOSPHERIC TECHNOLOGIES AND SCIENCES, INC.
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=2128443&HistoricalAwards=false
关键词：
Collaborative Research New Pathways Enhanced

项目摘要

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，即一层滑过另一层，可能会导致薄云层中常见的不稳定，就像一系列海浪在海滩上破裂一样。这些不稳定被称为开尔文-亥姆霍兹不稳定，在切变强烈的大气层和海洋中造成湍流和混合。在大气中，这些“巨浪”之间的距离可以从离地面几米到高度高达100公里的10公里或更大。在云层中看到的那些通常有从几百米到一公里左右的间隔(或波长)。这些巨浪“破裂”时的湍流和混合影响了大气结构和天气，特别是在地面附近，但它们的影响在天气预报模式中没有得到很好的描述。这项研究将探索最近在极高海拔的稀薄云中发现的一种导致破裂和湍流的新型不稳定，研究小组预计这种不稳定在所有海拔都会发生，并显著增加这些过程造成的湍流和混合。如果显示在更广泛的条件下发生，这将显著影响我们对地面附近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，当更充分地了解这些过程时，预计还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，他们拥有最先进的建模和超级计算经验。对高海拔(约80-90公里)极地中层云和气辉层的最新观测揭示了一种新类型的不稳定现象的发生，这种不稳定现象是由错误排列的Kelvin-Helmholtz(KH)巨浪伴随着变化的地球物理强迫而引起的。这些不稳定是由于相邻KH巨浪核心之间的相互作用而产生的，而不是在单个巨浪内部，对这些动力学的初步模拟表明，与没有它们时相比，它们要强得多，导致的湍流也更强烈。这些动力学来自于KH波流核心和大尺度涡管之间的相互作用，在KH波流由于初始条件而不对准或不连续的情况下被激发。使用直接数值模拟的初始建模能够对这些动力学、它们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和以前没有预料到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存在，它们将使我们能够更新这些动力学的建模方式，从而能够改进天气预报，并在海洋中做出类似的反应。由于KH不稳定性在其他物理领域也发挥着重要作用，特别是磁层物理和天体物理，这项研究的好处可能被证明是非常广泛的。这一奖项反映了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标准进行评估，被认为值得支持。