Impact of El Nino onset timing on the Indian Ocean: Pacific coupling and subsequent El Nino evolution

A relation between the timing of the El Nino onset and its subsequent evolution is examined by emphasizing its association with the Indian Ocean (IO) SST variation. Two types of El Nino events based on the timing of their onset are classified and their characteristics are examined and compared. In general, spring onset (SP) events grow greater in magnitude and their evolutions have a faster transition. On the contrary, summer onset (SU) events are relatively weaker in magnitude and have a slower transition. Moreover, in contrast to the SU events, the SP events have a strong tendency for accompanying an IO dipole and basin-wide type of warming pattern in the El Nino developing and mature phases, respectively. It is demonstrated here that the distinctive evolutions in transition phase of the two events are resulted from the difference in IO SST. The warm IO SST in the SP El Nino event, lead an anomalous easterlies over the western Pacific, which forces a fast termination of El Nino events.