Evolution of the Madden–Julian Oscillation in Two Types of El Niño

Abstract

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 predeveloping and developing phases of EP El Niño, but suppressed during the mature and decaying phases. In contrast, MJO activities do not show a clear relationship with CP El Niño before their occurrence over the western Pacific, but they increase 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 eastward propagation. Anomalous descending motions over the Maritime Continent and western Pacific related to El Niño can suppress convection and moisture flux convergence there and weaken MJO activities over these regions during the mature phase of both types of El Niño. MJO activities over the western Pacific are much weaker in EP El Niño due to the stronger anomalous descending motions. Furthermore, the MJO propagates more continuously and farther eastward during CP El Niño because of robust moisture convergence over the central Pacific, which provides adequate moisture for the development of MJO convection.

Further inquiry into characteristics of MJO in boreal winter

“…For a variable A, firstly, we calculate the long-time (from the start time to the end time) calendar mean for each day or month (Ā), and then subtract this climatology mean from the original data to get A ′ (A ′ = A −Ā); secondly, remove the long-time linear trend of A ′ by the least squares linear fitting (Wilks, 2006). The MJO signal was obtained using a 30-90 day Lanczos bandpass filter with 200 days smoothing (Duchon, 1979;Cai et al, 2013;Chen et al, 2016). The boreal winter in this article is from November to the following March.…”

“…The anomalous descending motion and moisture divergence are over the western Pacific, which weakens the convection and could not enhance the MJO activity. There is also enhanced convection over the eastern Pacific in weak MJO activity winter, which may lead to the enhanced ISO here, but such an enhanced ISO is a regional phenomenon that is unrelated to the eastward propagating MJO from the Indian Ocean to western Pacific (Chen et al ., ). Moreover, the SSTA also shows different features in strong and weak MJO active winter.…”

“…The percentage of MJO OLR is lower than the zonal wind, especially over the western Pacific region (Figure (b)). The interannual variability of MJO OLR also is strong over the central Pacific east to the 180°, which may be related to the ENSO event (Chen et al ., , ). However, both the MJO zonal wind at 850 hPa and OLR show that the MJO over the Indian Ocean and western Pacific has the maximum amplitude and significant interannual variability, although some differences exit between the zonal wind and OLR.…”

“…Moreover, the SSTA also shows different features in strong and weak MJO active winter. The SST is higher (lower) over the western (eastern) Pacific in strong MJO winter, indicating that the anomalous SST could impact the MJO by modulating the circulation and moisture anomalies (Kessler, ; Hendon et al ., ; Marshall et al ., ; Chen et al ., , ).…”

“…MJO activity has a significant impact on the global weather and climate. For example, the onset and break of the Asian‐Australian monsoon and its precipitation (Yang and Li, ; Zhang, ; Li et al ., ; Zhu and Li, , ); the occurrences of freezing rain, snow weather, and extremely heavy precipitation events (Jia et al ., ; Jones and Carvalho, ); the ENSO cycle (Kessler, ; Hendon et al ., ; Marshall et al ., ; Chen et al ., , ); and the genesis, intensity, tracks, and landfalls of tropical cyclones (Li and Zhou, , ; Zhu et al ., ). Investigation of the basic characteristics of MJO activity will not only help us understand the essential features of MJO and its influences accurately but also could improve the capability of its simulation and forecast.…”