Evolution of Madden-Julian Oscillation in two types of El Niño

Evolution characteristics of the Madden-Julian Oscillation (MJO) during 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 suppressed during the mature and decaying phases. In contrast, MJO activities do not show clear relationship with CP El Niño before its occurrence over the western Pacific, but increased over the central Pacific during the mature and decaying phases of CP El Niño. 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 for CP El Niño. EP El Niño tends to weaken the MJO and lead to a much shorter range of its eastwards propagation. Anomalous descending motions over the Maritime Continent and equatorial western Pacific related to El Niño can suppress convection and moisture convergence there, and weaken MJO activities in these regions during the mature phase of both types of El Niño. MJO activities are much weaker in EP El Niño due to the stronger anomalous descending motions. Furthermore, the MJO propagates more continuous and further eastward during CP El Niño because of robust moisture flux convergence over the central Pacific, which provides adequate moisture for the development of MJO convection.