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| Titel |
Interactions between almost unstable baroclinic waves and the tropical convection in aquaplanet simulations |
| VerfasserIn |
Giuseppe Zappa, Valerio Lucarini, Antonio Navarra |
| 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 |
250042113
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| Zusammenfassung |
| Simulations performed with the ECHAM5 GCM and the boundary conditions provided in the
control simulation of the aquaplanet intercomparison project feature a strong and persistent
wavenumber 5 signature. Such a mode peaks around 30 degrees, has a preferential symmetric
component between the two hemispheres, and a weak baroclinic zonal tilt. Moreover, a phase
lock with the tropical convection is observed. Previous works, mainly based on models
without an explicit convection, called for an inverse energy cascade as the process that feeds
energy in a wave 5 Rossby wave whose phase propagation is slowed down by the
interaction with the high frequency. The theory is here expanded by taking into
consideration the interaction with the tropical convection and the baroclinicity of the
system.
Spectra of the meridional wind velocity shows that the wave 5 component is
part of a well defined dispersion relation ranging from wave number 3 to 7 with
westward group velocity. A decrease in the mid-tropospheric temperature gradient
displaces the components toward a more eastward propagation, and leads to the
subsequent stabilization of wavenumber 6 and 7. The analysis of the cospectra of VT and
WT shows how the stabilised quasi-stationary component is a marginally stable
wave, transporting but only partially converting energy. These results are interpreted
in agreement with the Green’s model of baroclinic instability, and the Hoskins
and Karoly ray propagation’s theory. Moreover, the stationary, marginally stable
baroclinic wave can resonate with the tropical convection, thus becoming itself a
tropical-extratropical coupled unstable wave. The dynamic of the process of interaction is
discussed and its overall feedback on the energetic of the systems is evaluated. |
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