Characteristics of the frequency of wintertime Indian-Burma Trough events and its linkage with Tropical Indo-Pacific Sea surface temperature anomalies

The Indian-Burma Trough (IBT) can modulate winter precipitation across East and South Asia on various timescales, yet traditional climatological indices fail to capture its synoptic-scale variability. This study defines an event-based frequency index by objectively identifying the individual IBT events from 1981 to 2019, revealing an average of 18.3 events per winter that originate over the northern Bay of Bengal and propagate eastward along the subtropical westerlies. The interannual variability of IBT frequency is closely linked to a tripole pattern of the tropical Indo-Pacific sea surface temperature anomalies (SSTA), showing significant positive correlations with the SSTAs in tropical western Indian Ocean and central-eastern Pacific Ocean, and a negative correlation with the equatorial SSTAs east of the Philippines. This SST configuration modulates IBT frequency through dual pathways. (1) Tripole-organized Walker circulation suppresses convection near the Maritime Continent, triggering a northern Indian Ocean anticyclone that enhances westerlies and cyclonic vorticity over the Bay of Bengal for IBT occurrence. (2) SST-induced meridional thermal contrasts between the tropical Indo-Pacific Ocean, particularly the Indian Ocean, and the Tibetan Plateau regulate IBT formation via thermal wind-topography interactions.