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| Titel |
Gravity waves produced by the total solar eclipse of 1 August 2008 |
| VerfasserIn |
Julien Marty, Francis Dalaudier, Damien Ponceau, Elisabeth Blanc, Munkhuu Ulziibat |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040053
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| Zusammenfassung |
| Gravity waves are a major component of atmospheric small scale dynamics because of
their ability to transport energy and momentum over considerable distances and of
their interactions with the mean circulation or other waves. They produce pressure
variations which can be detected at the ground by microbarographs. The solar intensity
reduction which occurs in the atmosphere during solar eclipses is known to act
as a temporary source of large scale gravity waves. Despite decades of research,
observational evidence for a characteristic bow-wave response of the atmosphere to
eclipse passages remains elusive. A new versatile numerical model (Marty, J. and
Dalaudier, F.: Linear spectral numerical model for internal gravity wave propagation. J.
Atmos. Sci. (in press)) is presented and applied to the cooling of the atmosphere
during a solar eclipse. Calculated solutions appear to be in good agreement with
ground pressure fluctuations recorded during the total solar eclipse of 1 August
2008. To the knowledge of the authors, this is the first time that such a result is
presented.
A three-dimensional linear spectral numerical model is used to propagate internal gravity
wave fluctuations in a stably stratified atmosphere. The model is developed to get first-order
estimations of gravity wave fluctuations produced by identified sources. It is based on the
solutions of the linearized fundamental fluid equations and uses the fully-compressible
dispersion relation for inertia-gravity waves. The spectral implementation excludes
situations involving spatial variations of buoyancy frequency or background wind.
However density stratification variations are taken into account in the calculation of
fluctuation amplitudes. In addition to gravity wave packet free propagation, the
model handles both impulsive and continuous sources. It can account for spatial
and temporal variations of the sources allowing to cover a broad range of physical
situations.
It is applied to the case of solar eclipses, which are known to produce large-scale bow
waves on the Earth’s surface. The asymptotic response to a Gaussian thermal forcing
travelling at constant velocity as well as the transient response to the 4 December 2002
eclipse are presented. They show good agreement with previous numerical simulations. The
model is then applied to the case of the 1 August 2008 solar eclipse. Ground pressure
variations produced by the response to the solar intensity reduction in both stratosphere and
troposphere are calculated.
These synthetic signals are then compared to pressure variations recorded by IMS
(International Monitoring System) infrasound stations and a temporary network specifically
set up in Western Mongolia for this occasion. The pressure fluctuations produced by the 1
August 2008 solar eclipse are in a frequency band highly disturbed by atmospheric tides.
Pressure variations produced by atmospheric tides and synoptic disturbances are thus
characterized and removed from the signal. A low frequency wave starting just after the
passage of the eclipse is finally brought to light on all stations. Its frequency and amplitude
are close to the one calculated with our model, which strongly suggest that this signal was
produced by the total solar eclipse. |
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