Impacts of Summer Madden–Julian Oscillation Diversity on Multiple Tropical Cyclone Events over the Western North Pacific

Abstract While previous studies have extensively examined the Madden–Julian oscillation (MJO) influence on tropical cyclone (TC) activity, they often overlook the substantial diversity in MJO propagation behavior. This study addresses this gap by classifying summer MJO events into four distinct patterns—stationary (Stand), jumping (Jump), slow eastward propagating (Slow), and fast eastward propagating (Fast)—using a k -means clustering method. We investigate how each MJO pattern modulates the occurrence of multiple tropical cyclone events (MTCEs; multiple TC formations within 3 days) over the western North Pacific (WNP) and explore the associated physical mechanisms. Results show that the Slow and Fast patterns account for ∼80% of all MTCEs, with the Slow pattern contributing the most (59%). The Slow pattern is characterized by prolonged eastward propagation and a broad meridional extent, which enhances moisture convergence and ascending motion, thereby promoting widespread TC genesis. The Fast pattern is associated with a more zonally extended monsoon trough and enhanced vorticity stretching, supporting MTCE formation but with less clustering due to its rapid progression. In contrast, the Jump pattern exerts a weaker and more localized influence, while the Stand pattern—with convection confined to the Indian Ocean—has negligible impact. These results highlight the critical role of MJO diversity in shaping intraseasonal TC variability and offer insights for improving TC prediction over the WNP. Significance Statement The Madden–Julian oscillation (MJO), a crucial component of atmospheric intraseasonal variability, plays a pivotal role in modulating the genesis of multiple tropical cyclones (MTCs) over the western North Pacific, while exhibiting significant diversity in its behavior. This study investigates the physical mechanisms by which distinct MJO patterns influence the formation of MTC events. The results highlight the importance of recognizing MJO diversity for improving the prediction of multiple TC events during active typhoon seasons.