Collaborative Research: Inertially Unstable Currents and Internal Waves

合作研究：惯性不稳定电流和内波

• 批准号: 0525776
• 负责人: George Carnevale
• 金额: $ 24.62万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0525776&HistoricalAwards=false
• 关键词: Collaborative; Research; Inertially; Unstable; Currents

0525776/0526033Inertial instability has been widely studied in meteorology where it is considered a source of clearair turbulence, rain bands, squall lines and atmospheric gravity waves. It has received much lessattention in oceanography probably because it is generally thought to occur only for anticyclonically (clockwise) sheared parallel flows or anticyclones of strengths not typically observed in the ocean. However, there are many observations of anticyclonic currents in the ocean that are marginally stable, and this suggests that inertial instability may be the primary mechanism by which anticyclonic shear and anticyclonic vortices are maintained at stable or marginally stable values. The criterion for inertial instability is often quoted as Rossby number less than minus one, where a negative Rossby number implies anticyclonic flow However this criterion applies only to flows in homogeneous fluids like the mixed layer with no vertical shear In stratified flow that is vertically sheared as is commonly the case inertial instability can also occur with Rossby numbers between -1 and 0. Furthermore, even cyclonically sheared flows or cyclonic vortices for which Ro is greater than zero can be inertially unstable if the vertical shear is strong enough. It is also interesting that this instability can occur when the Richardson number is well above a quarter that is, in flows that are stable to the Kelvin Helmholtz instability, a controlling factor in oceanic flows. In other words, flows that are stable with regard to the well known Richardson number criterion can, in fact, be unstable because of inertial instability. It is therefore possible that inertial instability is frequently a controlling factor in oceanic flows without having been recognized as such. This renewal proposal will continue studies of inertial instability with the object of providing a fundamental basis for understanding the role that inertial instability plays in the worlds oceans. Under prior NSF funding, the investigators have performed a systematic numerical study of the effect of varying basic parameters on the inertial instability of idealized model vortices with no vertical shear and with weak vertical shear. In addition, the resulting analytical model, based on plane parallel horizontally sheared flow, is able to explain and predict much of the fundamental results of the numerical studies. From these investigations, there are now guidelines for exploring further. The previous studies will be extended to much more realistic models of oceanic vortices. Through a series of numerical simulations the effects of inertial instability will be studied in a variety of model vortices over a wide range of the essential parameters.Intellectual Merit: By undertaking our investigation of inertial instability, we hope to improve our understanding of the role that inertial instability plays in stabilization and maintenance of oceanic currents and eddies.Broader Impacts: As a broader impact, these studies should provide guidance for those attempting to develop parameterizations for ocean models and criteria for determining likely locations for intense internal wave generation and inertial instability. Because of the intrinsically small vertical scales of inertial instability, it is usually not resolved by ocean models. Thus, the simulated flows can become and stay inertially unstable. This unphysical behavior must be corrected to maintain currents in the models at physically realizable levels, but a proper parameterization of the effects of the instability can be obtained only through increased understanding. This collaborative research project will foster an international collaboration with professor Orlandi at the University of Rome and one of his graduate students.

0525776/0526033惯性不稳定性在气象学中得到了广泛的研究，它被认为是晴空湍流、雨带、飑线和大气重力波的来源。它在海洋学中受到的关注要少得多，可能是因为它通常被认为只发生在反气旋（顺时针）剪切平行流或强度通常在海洋中观察不到的反气旋中。然而，有许多观测结果表明，海洋中的反气旋流是边缘稳定的，这表明惯性不稳定可能是反气旋切变和反气旋涡旋保持稳定或边缘稳定值的主要机制。惯性不稳定性的判据通常被引用为小于负1的罗斯比数，其中负的罗斯比数意味着反气旋流。然而，该判据仅适用于均匀流体中的流动，如没有垂直剪切的混合层。在垂直剪切的分层流动中，通常情况下，罗斯比数在-1和0之间也会发生惯性不稳定性。 此外，如果垂直切变足够强，甚至Ro大于零的气旋性切变流或气旋性涡旋也可能是惯性不稳定的。 同样有趣的是，当Richardson数远高于四分之一时，也就是说，在对Kelvin Helmholtz不稳定性稳定的流动中，这种不稳定性可能发生，Kelvin Helmholtz不稳定性是海洋流动中的一个控制因素。换句话说，根据著名的理查森数准则是稳定的流动，实际上可能由于惯性不稳定性而不稳定。因此，惯性不稳定性可能经常是海洋流动中的一个控制因素，但人们并没有认识到这一点。这一更新提案将继续研究惯性不稳定性，目的是为了解惯性不稳定性在世界海洋中的作用提供基本依据。在先前的NSF资助下，研究人员对不同基本参数对无垂直剪切和弱垂直剪切的理想化模型涡的惯性不稳定性的影响进行了系统的数值研究。此外，由此产生的分析模型，平面平行水平剪切流的基础上，能够解释和预测的基本结果的数值研究。通过这些调查，现在有了进一步探索的指导方针。以前的研究将扩展到更现实的海洋涡旋模型。通过一系列的数值模拟，我们将研究惯性不稳定性在各种模式涡旋中的影响，这些模式涡旋的基本参数范围很广。智力上的优点：通过对惯性不稳定性的研究，我们希望提高我们对惯性不稳定性在稳定和维持洋流和涡旋中所起作用的理解。作为一个更广泛的影响，这些研究应该为那些试图为海洋模型制定参数的人提供指导，并为确定强烈内波生成和惯性不稳定的可能位置提供标准。由于惯性不稳定的垂直尺度很小，通常无法用海洋模式解决。因此，模拟的流动可以变得并保持惯性不稳定。这种非物理行为必须加以纠正，以保持在物理上可实现的水平在模型中的电流，但一个适当的参数化的不稳定性的影响，只能通过增加了解。这一合作研究项目将促进与罗马大学Orlandi教授及其一名研究生的国际合作。