OLR perspective on the Indian Ocean Dipole with application to East African precipitation

Interannual variability of precipitation over eastern Africa (Somalia, Ethiopia, and Kenya) is impacted by the Indian Ocean dipole (IOD), which has its maximum amplitude during autumn. During northern spring, sea‐surface temperature (SST) in the tropical Indian Ocean is nearly always sufficiently high to sustain convection, but it exhibits no clear pattern of variability. Thus, precipitation variability over Eastern Africa during spring is not connected to any Indian Ocean interannual mode sustained by SST anomalies. Yet, seasonal variability in atmospheric convection might sustain interannual modes during spring independent of SST. We construct an index for the IOD based on outgoing long‐wave radiation anomaly (OLRA) instead of SST anomaly. During northern spring, analysis of this index shows that interannual precipitation over Eastern Africa is correlated with interannual variability similar to the IOD, as measured by OLR. The largest part of that relationship originates from the western Indian Ocean, with smaller contributions from the eastern Indian Ocean. Results indicate that atmospheric convection over the tropical Indian Ocean couples the atmospheric circulation over the eastern and western Indian basin irrespective of SST anomalies. Results from constructed analogue analysis show that positive SST anomaly during northern winter caused by persistence of subsidence and cloud–radiation–SST negative feedback over the southeastern Indian Ocean from the previous positive IOD is associated with formation of negative IOD later during the following autumn.