Atmospheric and Oceanic Physics
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New submissions for Wed, 22 Mar 17
 [1] arXiv:1703.07254 [pdf, ps, other]

Title: Development of nonmodal shear induced instabilities in atmospheric tornadoesComments: 5 pages, 5 figuresSubjects: Atmospheric and Oceanic Physics (physics.aoph)
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 socalled Rankine vortex model; the BurgersRott 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 BurgersRott 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.
Crosslists for Wed, 22 Mar 17
 [2] arXiv:1703.06343 (crosslist from physics.fludyn) [pdf, ps, other]

Title: New conformal mapping for adaptive resolving of the complex singularities of Stokes waveSubjects: Fluid Dynamics (physics.fludyn); Numerical Analysis (math.NA); Pattern Formation and Solitons (nlin.PS); Atmospheric and Oceanic Physics (physics.aoph); Computational Physics (physics.compph)
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 (crosslist from physics.fludyn) [pdf, ps, other]

Title: Nonuniversal velocity probability densities in twodimensional turbulence: the effect of largescale dissipationAuthors: YueKin TsangJournalref: Phys. Fluids 22, 115102 (2010)Subjects: Fluid Dynamics (physics.fludyn); Atmospheric and Oceanic Physics (physics.aoph)
We show that some statistical properties of forced twodimensional turbulence have an important sensitivity to the form of largescale dissipation which is required to damp the inverse cascade. We consider three models of largescale dissipation: linear "Ekman" drag, nonlinear quadratic drag, and scale selective hypodrag that damps only lowwavenumber modes. In all cases, the statistically steady vorticity field is dominated by almost axisymmetric vortices, and the probability density function of vorticity is nonGaussian. However, in the case of linear and quadratic drag, we find that the velocity statistics is close to Gaussian, with nonnegligible contribution coming from the background turbulent flow. On the other hand, with hypodrag, the probability density function of velocity is nonGaussian and is predominantly determined by the properties of the vortices. With hypodrag, the relative positions of the vortices and the exponential distribution of the vortex extremum are important factors responsible for the nonGaussian 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 ModelsAuthors: Judith Berner, Ulrich Achatz, Lauriane Batte, Lisa Bengtsson, Alvaro De La Camara, Daan Crommelin, Hannah Christensen, Matteo Colangeli, Stamen Dolaptchiev, Christian L.E. Franzke, Petra Friederichs, Peter Imkeller, Heikki Jarvinen, Stephan Juricke, Vassili Kitsios, Franois Lott, Valerio Lucarini, Salil Mahajan, Timothy N. Palmer, Cecile Penland, JinSong Von Storch, Mirjana Sakradzija, Michael Weniger, Antje Weisheimer, Paul D. Williams, JunIchi YanoComments: 26 pages, 15 figures. Final published versionSubjects: Atmospheric and Oceanic Physics (physics.aoph); Computational Physics (physics.compph); Fluid Dynamics (physics.fludyn); Geophysics (physics.geoph)
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