MJO and CCEW modulation on South China Sea and Maritime Continent boreal winter subseasonal peak precipitation

Rainfall over South China Sea (SCS)-Maritime Continent (MC) region involves multiple-scale phenomena such as the annual cycle, monsoon variability, ENSO, Madden-Julian Oscillation (MJO), and convectively coupled equatorial waves (CCEWs). This study focuses on documenting MJO and CCEW modulation on the boreal winter subseasonal peak precipitation, which is an event with maximum 15-day accumulated rainfall amount during November to February, summarized at 10 by 10 degrees of longitude and latitude box areas in the region. It turns out that MJO shows strong influence on the peak event occurrence time. However, MJO has almost no positive effect on the peak event in the near equator land area. Mixed Rossby-gravity wave and tropical disturbance (MT) and equatorial Rossby (ER) wave show strong positive modulation on peak rainfall mean intensity. Cases during the SCS Two Island Monsoon Experiment (SCSTIMX) winters (2016/17 and 2017/18) are analyzed. To the north of 5 degrees N, the peak event in 2016/17 occurred concurrently with MJO convective phase, while in 2017/18 as lack of MJO activity the occurrence time was modulated by the ER wave. The 2016/17 peak event shows weaker mean rainfall intensity than the 2017/18 event. To the south of 5 degrees N, the area-mean peak event occurrence time was delayed in 2016/17, while the intensity was enhanced by the joint modulation of MJO, Kelvin and ER waves. The importance of understanding the area-mean and within-area-difference of peak rainfall events in the SCS-MC region was discussed. The findings can be applied to assess the subseasonal predictability of dynamical forecast models.