The spontaneous generation of inertia–gravity waves during frontogenesis forced by large strain: theory
The spontaneous generation of inertia–gravity waves during frontogenesis forced by large strain: theory
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大应变迫使锋生过程中惯性重力波的自发产生：理论
DOI：
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发表时间：
2014
影响因子：
3.7
通讯作者：
John R. Taylor
中科院分区：
文献类型：
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作者：
C. Shakespeare;John R. Taylor
摘要密度锋是海洋和大气边界层的共同特征。野外观测和数值模拟表明，锋面梯度的锐化，或锋生，可以自发地产生惯性重力波(IGW)。尽管在使用诸如准地转(Stone，J.Atmos)等近似方法描述锋生过程方面取得了重大进展。《科学》，第23卷，1966年，第455-565页，Williams&Plotkin J.Atmos。科学，第25卷，1968年，第201-206页)半地转(Hoskins，Annu.流体机械修订版，第14卷，1982，第131-151页)，这些模型省略了波。在这里，我们进一步发展了莎士比亚和泰勒的分析模型(J.Fluid Mech，Vol.736,2013，pp.366-413)来描述初始地转平衡锋在时变水平应变下的IGW自发辐射。该模型使用了无限长的直线锋面和均匀位涡(PV)流体的理想构型，在锋面上施加了均匀的收敛应变，类似于Hoskins&Bretherton(J.Atmos)。科学，第29卷，1972年，第11-37页)。惯性重力波是通过两种不同的机制产生的：大尺度气流的加速和锋面崩塌。对于较小的应变值，通过锋面塌陷产生的波被预测为指数级小，但对于较大的应变值则是显著的。时变应变还可以通过加速跨锋气流和破坏地转平衡来产生有限幅度的波。在这两种情况下，波都被迎面而来的应变流捕获，只有当应变场充分减弱时，波才能从前锋区传播出去，导致波的发射在时间和空间上都是强烈局部化的。
Abstract Density fronts are common features of ocean and atmosphere boundary layers. Field observations and numerical simulations have shown that the sharpening of frontal gradients, or frontogenesis, can spontaneously generate inertia–gravity waves (IGWs). Although significant progress has been made in describing frontogenesis using approximations such as quasi-geostrophy (Stone, J. Atmos. Sci., vol. 23, 1966, pp. 455–565, Williams & Plotkin J. Atmos. Sci., vol. 25, 1968, pp. 201–206) semi-geostrophy (Hoskins, Annu. Rev. Fluid Mech., vol. 14, 1982, pp. 131–151), these models omit waves. Here, we further develop the analytical model of Shakespeare & Taylor (J. Fluid Mech., vol. 736, 2013, pp. 366–413) to describe the spontaneous emission of IGWs from an initially geostrophically balanced front subjected to a time-varying horizontal strain. The model uses the idealised configuration of an infinitely long, straight front and uniform potential vorticity (PV) fluid, with a uniform imposed convergent strain across the front, similar to Hoskins & Bretherton (J. Atmos. Sci., vol. 29, 1972, pp. 11–37). Inertia–gravity waves are generated via two distinct mechanisms: acceleration of the large-scale flow and frontal collapse. Wave emission via frontal collapse is predicted to be exponentially small for small values of strain but significant for larger strains. Time-varying strain can also generate finite-amplitude waves by accelerating the cross-front flow and disrupting geostrophic balance. In both cases waves are trapped by the oncoming strain flow and can only propagate away from the frontal zone when the strain field weakens sufficiently, leading to wave emission that is strongly localised in both time and space.
影响因子：
3.7
作者：
Eric Danioux;J. Vanneste;P. Klein;H. Sasaki
通讯作者：
Eric Danioux;J. Vanneste;P. Klein;H. Sasaki