Response of regional circulation features to the Indian Ocean dipole and influence on Central Africa climate

The time-varying September-November relationship between the Indian Ocean Dipole (IOD) and Central African (CA) rainfall has strengthened since the 1990s, implying an increasing IOD influence over CA rainfall. Using observational and reanalysis datasets covering the 1980–2016 period, this study examines the CA circulation response associated with the Indian Ocean dynamics during the September-December IOD events, since this circulation constitutes a key moisture transport feature for CA rainfall variability. The results show that during positive IOD events (pIOD), the moisture transport drivers over CA and the Indian Ocean (IO) are synchronous, leading to an increase in CA rainfall, whereas the reverse pattern is observed during negative IOD events (nIOD). The equatorial easterly (westerly) moisture transport driven by the anticyclonic (cyclonic) circulation in the northern tropical IO and the weakening (intensification) of the African Easterly Jet’s northern component (AEJ-N), leads to an increase (decrease) in CA rainfall during pIOD (nIOD). Warm (cold) SST anomalies in the eastern Indian Ocean during nIOD (pIOD) event, intensify (weaken) the large-scale upward motion, strengthening (weakening) the cyclonic circulation in the mid-troposphere, thus favoring a significant westerly (easterly) circulation. The AEJ-N weakening during pIOD events is associated with a strengthening of the meridional pressure gradient and a westward shift in the Saharan high location at the AEJ-N’s northern edge. The results also reveal a significant influence of the Atlantic during pIOD events, induced by its teleconnection with the IO, whose effects are more modulated by the IOD’s western pole warming than by the IOD-related SST gradient.