Impact of organized intraseasonal convective perturbations on the tropical circulation

Hugo Bellenger (1) , Jean-Philippe Duvel (1) , Matthieu Lengaigne (2) , Phu Levan (1)

1 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
2 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques

Using an atmospheric Global Circulation Model (GCM), we study the dynamical response of the tropical atmosphere to large-scale convective perturbations. We hypothesize that such perturbations can be triggered by intraseasonal SST anomalies. We thus compare two ensembles of simulations forced either with actual daily SST fields (high frequency, HF) or with low-pass filtered SST fields (T > 90 days; low frequency, LF). In HF simulations, there is a small increase of seasonal mean precipitation, but a strong and statistically significant increase of the low-level westerly flow. It is argued that it is mostly the "aggregation" of the convection into a few large-scale organized intraseasonal events, and not the intensification of the seasonal mean precipitation, that acts to intensify the low-level westerly flow in the HF simulations. This non-linear behavior shows that a correct representation of intraseasonal variability is required for a correct simulation of the average tropical circulation.

Mots clés: Atmospheric Processes: Climatology; Atmospheric Processes: General circulation (1223)

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]

Hugo Bellenger, Jean-Philippe Duvel, Matthieu Lengaigne, Phu Levan. Impact of organized intraseasonal convective perturbations on the tropical circulation. Geophysical Research Letters, 2009, 36, pp.16703. ⟨10.1029/2009GL039584⟩. ⟨hal-00760004⟩