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| Titel |
The Interaction between Meso- and Sub-mesoscale Gravity Waves in Boussinesq Dynamics |
| VerfasserIn |
Jannik Wilhelm, Gergely Bölöni, Triantaphyllos R. Akylas, Junhong Wei, Bruno Ribstein, Rupert Klein, Ulrich Achatz |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144846
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| Publikation (Nr.) |
 EGU/EGU2017-8720.pdf |
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| Zusammenfassung |
| Nowadays, high-resolution numerical weather prediction (NWP) models are resolving the
mesoscale part of the gravity wave (GW) spectrum, while the effect of small sub-gridscale
GWs is not taken into account, although there are indications that the GW momentum flux
associated with the small-scale waves might have relevant contributions to the energy
budget. In contrast to the situation when GW parameterisations were developed for
interactions of (mesoscale) GWs with a synoptic-scale flow, unresolved GWs propagate
now in a background which includes resolved mesoscale GWs. Consequently, it is
necessary to reconsider the basic theory, which GW parameterisations are based on, and
study the interaction between meso- and sub-mesoscale GWs theoretically and
numerically.
A multi-scale asymptotic analysis is applied in Boussinesq dynamics in order to identify
regimes for this interaction, characterised by the amplitude and aspect ratio of small-scale
waves, and the ratio of Coriolis parameter and Brunt-Väisälä frequency, where powers of
the latter are acting as the scale separation parameter [1]. It is found that mesoscale waves
are mainly influenced by the vertical flux of horizontal momentum associated
with the sub-mesoscale waves. Moreover, the sub-mesoscale GW field is able to
produce mesoscale wind patterns far away from itself, connected to a resonance
phenomenon known from wave-wave interaction theory [2]. As variations of background
stratification and mesoscale wind patterns also impact the characteristics of the
sub-mesoscale wave field, a two-way coupling occurs that can be studied by a WKB ray
tracer as a transient GW parameterisation. Indeed, it has recently been shown
that a weakly nonlinear coupling can be described very well by a phase space
Lagrangian WKB ray tracer [3]. Beyond that, the role of wave breaking in the
wave-mean flow interaction has been found to only be of secondary importance
[4].
Fully nonlinear Large Eddy Simulations (LES), resolving also sub-mesoscale
wave structures, confirm our theoretical findings and validate the phase space
approach of the Lagrangian WKB ray tracer for vertically as well as horizontally
confined (2D) wave fields. The theory and the corresponding ray tracer will be
described, and validating numerical simulations will be shown. Several cases will be
discussed, exhibiting e.g. the radiation of a mesoscale GW by a sub-mesoscale GW
packet.
References
[1] U. Achatz, B. Ribstein, F. Senf, R. Klein, 2016. The interaction between synoptic-scale
balanced flow and a finite-amplitude mesoscale wave field throughout all atmospheric layers:
Weak and moderately strong stratification. Quart. J. Roy. Met. Soc., Accepted.
[2] A. Tabaei, T.R. Akylas, 2007. Resonant Long-Short Wave Interactions in an Unbounded
Rotating Stratified Fluid. Stud. Appl. Math., 119, 271-296.
[3] J. Muraschko, M.D. Fruman, U. Achatz, S. Hickel, Y. Toledo, 2015. On the application
of Wentzel-Kramer-Brioullin theory for the simulation of the weakly nonlinear dynamics of
gravity waves. Quart. J. Roy. Met. Soc., 141, 676-697.
[4] G. Bölöni, B. Ribstein, J. Muraschko, C. Sgoff, J. Wei, U. Achatz, 2016. The interaction
between atmospheric gravity waves and large-scale flows: an efficient description beyond the
non-acceleration paradigm. J. Atm. Sci., Accepted. |
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