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| Titel |
3D DNS and LES of Breaking Inertia-Gravity Waves |
| VerfasserIn |
S. Remmler, M. D. Fruman, S. Hickel, U. Achatz |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062843
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| Zusammenfassung |
| As inertia-gravity waves we refer to gravity waves that have a sufficiently low frequency and
correspondingly large horizontal wavelength to be strongly influenced by the Coriolis force.
Inertia-gravity waves are very active in the middle atmosphere and their breaking is
potentially an important influence on the circulation in this region. The parametrization of
this process requires a good theoretical understanding, which we want to enhance with the
present study.
Primary linear instabilities of an inertia-gravity wave and “2.5-dimensional”
nonlinear simulations (where the spatial dependence is two dimensional but the
velocity and vorticity fields are three-dimensional) with the wave perturbed by its
leading primary instabilities by Achatz [1] have shown that the breaking differs
significantly from that of high-frequency gravity waves due to the strongly sheared
component of velocity perpendicular to the plane of wave-propagation. Fruman & Achatz
[2] investigated the three-dimensionalization of the breaking by computing the
secondary linear instabilities of the same waves using singular vector analysis.
These secondary instabilities are variations perpendicular to the direction of the
primary perturbation and the wave itself, and their wavelengths are an order of
magnitude shorter than both. In continuation of this work, we carried out fully
three-dimensional nonlinear simulations of inertia-gravity waves perturbed by their
leading primary and secondary instabilities. The direct numerical simulation (DNS)
was made tractable by restricting the domain size to the dominant scales selected
by the linear analyses. The study includes both convectively stable and unstable
waves.
To the best of our knowledge, this is the first fully three-dimensional nonlinear direct
numerical simulation of inertia-gravity waves at realistic Reynolds numbers with complete
resolution of the smallest turbulence scales. Previous simulations either were restricted to
high frequency gravity waves (e. g. Fritts et al. [3]), or the ratio N-f was artificially
reduced (e. g. Lelong & Dunkerton [4]). The present simulations give us insight into
the three-dimensional breaking process as well as the emerging turbulence. We
assess the possibility of reducing the computational costs of three-dimensional
simulations by using an implicit turbulence subgrid-scale parametrization based
on the Adaptive Local Deconvolution Method (ALDM) for stratified turbulence
[5].
In addition, we have performed ensembles of nonlinear 2.5-dimensional DNS, like those
in Achatz [1] but with a small amount of noise superposed to the initial state, and
compared the results with coarse-resolution simulations using either ALDM as
well as with standard LES schemes. We found that the results of the models with
parametrized turbulence, which are orders of magnitude more computationally economical
than the DNS, compare favorably with the DNS in terms of the decay of the wave
amplitude with time (the quantity most important for application to gravity-wave drag
parametrization) suggesting that they may be trusted in future simulations of gravity wave
breaking.
References
[1]   U. Achatz. The primary nonlinear dynamics of modal and nonmodal
perturbations of monochromatic inertia gravity waves. J. Atmos. Sci., 64:74, 2007.
[2]   M. Fruman and U. Achatz. Secondary instabilities in breaking inertia-gravity
waves. J. Atmos. Sci., 69:303–322, 2012.
[3]   D. C. Fritts, L. Wang, J. Werne, T. Lund, and K. Wan. Gravity wave
instability dynamics at high reynolds numbers. Parts I and II. J. Atmos. Sci.,
66(5):1126–1171, 2009.
[4]   M.-P. Lelong and T. J. Dunkerton. Inertia-gravity wave breaking in three
dimensions. Parts I and II. J. Atmos. Sci., 55:2473–2501, 1998.
[5]   S. Remmler and S. Hickel. Spectral structure of stratified turbulence: Direct
numerical simulations and predictions by LES. Theor. Comput. Fluid Dyn.,
submitted, 2012. |
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