Multi-scale study of the rainy season onset over the Sudano-Sahelian belt: Spatial coherence and potential predictability

Romain Marteau (1) , Vincent Moron (2, 3, 4) , Nathalie Philippon (1) , Bernard Fontaine (1)

1 CRC - Centre de Recherches de Climatologie
2 IRI - International Research Institute for Climate and Society
3 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
4 IUF - Institut universitaire de France

The spatial coherence of boreal monsoon onset (July-September) over the western and central Sahel is studied through the analysis of daily rainfall records for 136 rain-gauges from 1950-2000. Onset of the rainy season has been defined using 3 definitions which rely on 3 overlapped spatial scales: (i) the regional scale, i.e. the northward ITCZ jump from Guinean to Soudano-Sahelian latitudes, (ii) the meso-scale related with the first occurrence of the main rainfall-generating phenomenon, that is squall line and (iii) the local-scale of the first rainfall recorded at the rain-gauge. Local and meso-scale onsets show a weak degree of instantaneous and inter-annual spatial coherence, meaning that onset is almost never simultaneously recorded across a regional network but also that its inter-annual variability is not in-phase across such area. In consequence, the seasonal predictability of the monsoon onset coming from planetary and zonal sea surface temperature variations is weak.

Mots clés: Onset of the rainy season; Sahel; Spatial coherence; predictability

Domaines: Climatologie; Milieux et Changements globaux

Romain Marteau, Vincent Moron, Nathalie Philippon, Bernard Fontaine. Multi-scale study of the rainy season onset over the Sudano-Sahelian belt: Spatial coherence and potential predictability. European Geosciences Union (EGU), Apr 2011, Vienne, Austria. ⟨hal-00584852⟩