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| Titel |
Assessment of the Impact of Middle-Atmosphere Solar Tides on Gravity Waves in a WKB Gravity-Wave Model Based on Wave-Action Phase-Space Density |
| VerfasserIn |
Bruno Ribstein, Ulrich Achatz, Fabian Senf |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091450
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| Publikation (Nr.) |
 EGU/EGU2014-5744.pdf |
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| Zusammenfassung |
| abstract
Gravity waves (GWs) and solar tides (STs) are main constituents of the dynamical coupling
between troposphere and mesosphere-lower-thermosphere (MLT). Via momentum deposition,
GWs control to a large extent the mesospheric mean circulation. STs are large scale waves,
mostly due to tropospheric and stratospheric diurnal heating processes, that modulate all
dynamical fields in the mesosphere. GWs ant STs also interact strongly with each
other.
Conventional GW parameterizations used to describe this interaction (e.g. [1]) neglect the
time-dependence and horizontal gradients of the background flow, with fatal effects (e.g. [2]).
We study here the propagation of GWs in a time-dependent middle-atmosphere background
flow, using a new (caustics free) WKB GW model (ray tracer). The background flow is
composed by a climatological mean and tidal fields extracted from a general circulation
model (HAMMONIA, see [3]). In order to avoid caustics, inevitable in classic ray-tracer
implementations, we implemented a new wave-action phase-space density conservation
scheme [4, 5]. The scheme attaches to each ray a finite volume in the location &
wavenumber phase-space. The location-wavenumber volume is conserved during the
propagation, responding in shape to the local stretching and squeezing in wave-number
space. From the propagation of GWs we evaluate the deposition of momentum
and buoyancy. Rayleigh-friction and temperature-relaxation coefficients are also
evaluated.
In this extension of the study by [2] it is shown, with an amplitude scheme more stable
against numerical instabilities, due to the avoidance of caustics, that STs (and so the
time dependence of the background flow) modulate the propagation of GWs. Via
Rayleigh-friction and temperature-relaxation coefficients, we also quantify how the
pseudo-momentum-, momentum-, and enthalpy-deposition of GWs can influence the
amplitude and the phase structure of STs. Finally, we compare momentum and
buoyancy fluxes from the propagation of GWs with results from a simple scale
analysis of the problem. These explain the amplitudes obtained by the scheme quite
well.
Key words: Middle-Atmosphere dynamics, Solar Tides, Gravity Waves, WKB model
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References :
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Res., 104:4223–4239, 1999.
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2011.
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Fomichev, D. Kinnison, D. Marsh, and S. Walters. The hammonia chemistry climate model:
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Meteorol. Soc., submitted, 2014. |
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