Accueil > Actualités > Séminaires > Séminaire de Paul Kushner au LMD-ENS


Titre : Stationary Wave Influence on Extratropical Variability
Nom du conférencier : Paul Kushner
Son affiliation : University of Toronto
Laboratoire organisateur : LMD
Date et heure : 23-07-2012 14h00
Lieu : Salle E314 du Département des Géosciences, ENS, 24 rue Lhomond, 75005 Paris
Résumé :

The zonal mean extratropical circulation and its variability are driven by interactions between the zonal mean circulation and large-scale waves. In this talk I will discuss how variability in the amplitude of the climatological stationary wave pattern can be an important source of variability in large-scale wave driving. This effect has been called "linear interference". It is apparent in observed polar stratospheric circulation variability and its coupling to the troposphere, as well as in other settings. A linear interference analysis can explain some surprising general circulation modelling (GCM) results. For example, in one set of simulations, externally forced Tropical East Pacific Ocean warming induces Arctic stratospheric warming and a negative Arctic Oscillation response, while Tropical Indian Ocean warming induces an opposite Arctic response. The Arctic response is sensitive to the location of the tropical warming because the forced wave amplifies the stationary wave pattern for the Pacific case but attenuates the stationary wave pattern for the Indian Ocean case. Linear interference effects are also found in GCM studies where extratropical surface cooling or snow forcing are used to drive atmospheric circulation anomalies. Interestingly, a counterexample, where linear interference is secondary, has been found in the stratospheric response to sea ice perturbations. I speculate that inconsistencies in GCM simulations of stationary waves might be a source of spread in extratropical zonal mean responses to climate forcings.

Contact :

Riwal Plougonven, LMD-ENS, Paris
01 44 32 27 31