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Abstract:
The Indian Summer Monsoon (ISM) and the West African Monsoon (WAM) are dominant drivers of boreal summer precipitation variability in tropical and subtropical regions. Although the regional precipitation dynamics in these two regions have been extensively studied, the intraseasonal interactions between the ISM and WAM remain poorly understood. Here, we employ a climate network approach based on extreme rainfall events to uncover synchronously occurring extreme rainfall patterns across the two monsoon systems. We reveal strong synchronization of extreme rainfall events during the peak monsoon period in July and August, linking heavy rainfall over North India to that over the Sahel with a lag of around 12 days. We find that La Niña like conditions in combination with the Boreal Summer Intraseasonal Oscillation (BSISO) and an enhanced Tropical Easterly Jet (TEJ) foster the synchronization between the ISM and the WAM. The northward-propagating BSISO triggers African Easterly Wave activity, bounded between a reduced African Easterly Jet and the TEJ. These induce westward-traveling anomalous deep convection over the Sahel, which causes extreme rainfall events to occur.
