Impact of Madden-Julian Oscillation on Persistent Heavy Rainfall over Hainan Island in October

LIU Yu; WU Hui; CAI Qinbo; WU Zhiyan; FENG Xiao

doi:10.16032/j.issn.1004-4965.2025.008

Abstract：This paper examined the influence of Madden-Julian Oscillation(MJO)on persistent heavy rainfall(PHR)over Hainan Island from 1979 to 2019.The results reveal that both the precipitation amount and frequency of PHR events peaked in October,exhibiting significant modulation by strong MJO activities.When MJO convection was active over the tropical Eastern Indian Ocean-Western Pacific(phases 3-6),PHR events over Hainan Island increased.Conversely,when MJO convection was located over the tropical Western Indian Ocean and the Central Pacific(phases 7,8,1,and 2),PHR events decreased.Active MJO convection in phases 3-6 induced anomalous easterly over Hainan Island,with northeasterly wind anomalies to the north and a cyclonic circulation anomaly over the north-central South China Sea.These conditions were consistent with the typical circulation mode of autumnal rainstorms over Hainan Island,which enhanced the low-frequency moisture flux convergence and thus moistened the lower atmosphere,favoring the occurrence and persistence of PHR over Hainan Island.In contrast,when MJO convection was active in phases 7,8,1,and 2,the anticyclonic circulation coupled with MJO convection over Hainan Island could limit moisture flux convergence and inhibit lower atmospheric moistening.The warmer sea surface temperatures(SST)in the tropical Eastern Indian Ocean-Western Pacific and the cooler SST in the tropical Eastern Pacific contributed to the local MJO convection in phases 3-6,which could strengthen the PHR events over Hainan Island.