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| Titel |
Quasi-geostrophic dynamics of a finite-depth tropopause |
| VerfasserIn |
Riwal Plougonven, Jacques Vanneste |
| 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 |
250038955
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| Zusammenfassung |
| The tropopause plays a crucial role in the dynamics of the atmosphere and simplified models
of its balanced dynamics have been obtained using the fact that it corresponds to a sharp
transition in stratification. The crudest model consists of describing the tropopause within the
quasi-geostrophic approximation as a rigid lid, yielding a surface quasi-geostrophic (SQG)
model. The rigid-lid assumption was relaxed by Juckes (1994) who replaced it by the more
realistic assumption of a finite jump in the stratification at the tropopause. The resulting
model remains the SQG model, with a relationship between potential-temperature and
velocity that involves the Brunt-Väisälä frequency N both of the troposphere and of the
stratosphere.
Here we relax the assumption of a vertical jump in stratification at the tropopause and
investigate the effect of the internal structure of the tropopause, both in stratification and in
shear. Using matched asymptotic expansions, we derive next-order corrections to the SQG
model of the tropopause. The model obtained remains three-dimensional, but is focused on
the dynamics of the tropopause region, with a simplified inversion relation to obtain the flow
outside of that region.
Our reduced model is then applied to study the dynamics of linear perturbations to the
tropopause. Edge waves are recovered to leading order, with a correction to the frequency
at next order. The sensitivity of this correction to the stratification jump, to the
structure of the transition and to the shear are discussed. Now, our model has richer
dynamics than the SQG model of the tropopause as it also includes a continuous
spectrum of sheared disturbances with no net integral of PV across the tropopause.
We show how they coexist with edge waves, how they decay with time because
of the shear, and how an arbitrary condition splits into edge waves and sheared
disturbances. |
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