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Abstract:
Since the Madden-Julian Oscillation (MJO) is a pillar of the subseasonal predictability, the continuity from one MJO event to another (successive events) and the emergence of a MJO event without an immediately preceding event (primary events) are of interest. What are the differences between the evolutions and intensities of primary and successive events? What determines the continuity or termination of a MJO event? The analysis is focused on austral summer, the season of strongest MJO events. The composite evolutions of 29 primary events and 27 successive events are analyzed considering the starting location over the Indian Ocean. Convection and circulation anomalies are characterized for MJO continuing or terminating events. The continuity involves MJO convective anomalies and teleconnections over the Western Hemisphere at the end of a cycle and beginning of the next. Influence function analysis of an extended vorticity equation model and simulations indicate a link between the anomalous convection over tropical/subtropical central South Pacific and South America (SA), while convection anomalies over SA produce tropical/extratropical teleconnections over Atlantic-Africa, favoring the restart of the MJO over Indian Ocean. Precursor signals associated with these links are strongly present in successive events, but much weaker before primary events, although bearing resemblance. Successive MJO events are much stronger than primary events, especially in the first half of the cycle. MJO events that terminate into neutral conditions exhibit very weak convective anomalies over the Central Pacific and SA at the end of the cycle, thus cutting the connection with the beginning of another cycle.
