Different evolution of Madden-Julian Oscillation in two types of El Niño

Abstract:

Different evolution characteristics of the Madden-Julian Oscillation (MJO) in the eastern Pacific (EP) and central Pacific (CP) types of El Niño have been investigated. MJO activities are strengthened over the western Pacific during the pre-developing and developing phases of EP El Niño, but they are suppressed in the mature and decaying phases. In contrast, MJO activities over the western Pacific have little relationship with CP El Niño before its occurrence, but increased over central Pacific during its mature and decaying phases. Lag correlation analyses further confirm that MJO activities over the western Pacific in boreal spring and early summer are closely related to EP El Niño up to 2-11 months later, but not to CP El Niño. EP El Niño tends to weaken the MJO and make its eastwards propagation range shorter. Anomalous descending motions over the Maritime Continent and equatorial western Pacific induced by El Niño decrease convection and moisture convergence in these areas, and lead to the weakened MJO activities during the mature phase of El Niño. The MJO activities are much weaker in EP El Niño due to the stronger anomalous descending motions in EP El Niño. Furthermore, the MJO propagates further eastward during CP El Niño because of robust moisture convergence in the central Pacific which provides adequate moisture for the development of MJO convection there.