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| Titel |
Intermittency of gravity-wave momentum flux in the stratosphere |
| VerfasserIn |
A. Hertzog, M. J. Alexander, R. Plougonven |
| 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 |
250059653
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| Zusammenfassung |
| Atmospheric gravity waves transfer energy and momentum from the troposphere to upper
layers of the atmosphere. They significantly contribute to forcing the global-scale Brewer
Dobson circulation in the middle atmosphere, and to driving the stratosphere out of radiative
equilibrium. As most of the gravity waves are not explicitly resolved in current
climate models, their effects on the general circulation must be parameterized. Strong
assumptions are generally used in such parameterizations, like for instance constant and
homogeneous non-orographic gravity-wave sources. In this study, we challenge this latter
hypothesis, and use long-duration balloon- and space-borne observations as well as
mesoscale numerical simulations to characterize the intermittency of gravity waves in
the lower stratosphere above Antarctica. This is achieved through working on the
gravity-wave momentum-flux probability density functions (pdfs) obtained with these three
datasets. The pdfs consistently exhibit long tails associated with the occurrence
of rare and large amplitude events. We provide a measure of the contribution of
these events to the total gravity-wave momentum flux, and show that only a small
fraction of the wavepackets are responsible for most of the momentum transport
during the winter regime of the stratospheric circulation. On the other hand, the
wave intermittency significantly decreases when stratospheric easterlies develop in
late spring and summer. With the exception of mountainous areas in winter, the
momentum-flux pdfs furthermore tend to behave like lognormal distributions. We
find that this behaviour can result from the propagation of a wave spectrum into a
varying background wind field that generates the occurrence of frequent critical
levels. |
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