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Atmospheric and Oceanic Physics

New submissions

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New submissions for Wed, 22 Mar 17

[1]  arXiv:1703.07254 [pdf, ps, other]
Title: Development of non-modal shear induced instabilities in atmospheric tornadoes
Comments: 5 pages, 5 figures
Subjects: Atmospheric and Oceanic Physics (physics.ao-ph)

In this paper we consider the role of nonmodal instabilities in the dynamics of atmospheric tornadoes. For this purpose we consider the Euler equation, continuity equation and the equation of state and linearise them. As an example we study several different velocity profiles: the so-called Rankine vortex model; the Burgers-Rott vortex model; Sullivan and modified Sullivan vortex models. It has been shown that in the two dimensional Rankine vortex model no instability appears in the inner region of a tornado. On the contrary, outside this area the physical system undergoes strong exponential instability. We have found that initially perturbed velocity components lead to amplified sound wave excitations. The similar results have been shown in Burgers-Rott vortex model as well. As it was numerically estimated, in this case, the unstable wave increases its energy by a factor of $400$ only in $\sim 0.5$min. According to the numerical study, in Sullivan and modified Sullivan models, the instability does not differ much by the growth. Despite the fact that in the inner area the exponential instability does not appear in a purely two dimensional case, we have found that in the modified Sullivan vortex even a small contribution from vertical velocities can drive unstable nonmodal waves.

Cross-lists for Wed, 22 Mar 17

[2]  arXiv:1703.06343 (cross-list from physics.flu-dyn) [pdf, ps, other]
Title: New conformal mapping for adaptive resolving of the complex singularities of Stokes wave
Subjects: Fluid Dynamics (physics.flu-dyn); Numerical Analysis (math.NA); Pattern Formation and Solitons (nlin.PS); Atmospheric and Oceanic Physics (physics.ao-ph); Computational Physics (physics.comp-ph)

A new highly efficient method is developed for computation of traveling periodic waves (Stokes waves) on the free surface of deep water. A convergence of numerical approximation is determined by the complex singularites above the free surface for the analytical continuation of the travelling wave into the complex plane. An auxiliary conformal mapping is introduced which moves singularities away from the free surface thus dramatically speeding up numerical convergence by adapting the numerical grid for resolving singularities while being consistent with the fluid dynamics. The efficiency of that conformal mapping is demonstrated for Stokes wave approaching the limiting Stokes wave (the wave of the greatest height) which significantly expands the family of numerically accessible solutions. It allows to provide a detailed study of the oscillatory approach of these solutions to the limiting wave. Generalizations of the conformal mapping to resolve multiple singularities are also introduced.

[3]  arXiv:1703.07000 (cross-list from physics.flu-dyn) [pdf, ps, other]
Title: Non-universal velocity probability densities in two-dimensional turbulence: the effect of large-scale dissipation
Authors: Yue-Kin Tsang
Journal-ref: Phys. Fluids 22, 115102 (2010)
Subjects: Fluid Dynamics (physics.flu-dyn); Atmospheric and Oceanic Physics (physics.ao-ph)

We show that some statistical properties of forced two-dimensional turbulence have an important sensitivity to the form of large-scale dissipation which is required to damp the inverse cascade. We consider three models of large-scale dissipation: linear "Ekman" drag, non-linear quadratic drag, and scale selective hypo-drag that damps only low-wavenumber modes. In all cases, the statistically steady vorticity field is dominated by almost axisymmetric vortices, and the probability density function of vorticity is non-Gaussian. However, in the case of linear and quadratic drag, we find that the velocity statistics is close to Gaussian, with non-negligible contribution coming from the background turbulent flow. On the other hand, with hypo-drag, the probability density function of velocity is non-Gaussian and is predominantly determined by the properties of the vortices. With hypo-drag, the relative positions of the vortices and the exponential distribution of the vortex extremum are important factors responsible for the non-Gaussian velocity statistics.

Replacements for Wed, 22 Mar 17

[4]  arXiv:1510.08682 (replaced) [pdf]
Title: Stochastic Parameterization: Towards a new view of Weather and Climate Models
Comments: 26 pages, 15 figures. Final published version
Subjects: Atmospheric and Oceanic Physics (physics.ao-ph); Computational Physics (physics.comp-ph); Fluid Dynamics (physics.flu-dyn); Geophysics (physics.geo-ph)
[ total of 4 entries: 1-4 ]
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