Distinct Influence of Different Boreal Summer Intraseasonal Oscillation Modes on Western North Pacific Tropical Cyclone Activity

Recent studies have identified three distinct modes of propagation associated with the boreal summer intraseasonal oscillation (BSiSO): canonical (northeastward), northward dipole, and eastward expansion. However, the impacts of these three BSiSO modes on western North Pacific tropical cyclone (TC) activity remain unclear. To address this question, we identified 98 BSiSO events during the boreal summer from 1979 to 2021, comprising 47 canonical, 26 northward dipole, and 25 eastward expansion events. in terms of TC genesis, the canonical and eastward expansion modes primarily influence TC genesis over the South China Sea, whereas the northward dipole mode modulates TC genesis across the western North Pacific. These differences arise from BSiSO-driven shifts in the large-scale environment and associated monsoon trough displacement. in terms of TC tracks and regional impacts, TCs tied to the canonical mode disproportionately affect southern China, whereas those linked to the northward dipole mode more strongly impact eastern China. The meridional migration of synoptic-scale waves and the zonal shift of the western Pacific subtropical high underpin the observed TC impacts across China driven by various BSiSO modes. These findings highlight the distinct modulation of TC activity by different BSISO modes and offer useful insights for intraseasonal TC forecasting.