Intraseasonal Variability of Apparent Heat Source over the Arabian Sea and Its Relationship with East Asian Summer Precipitation

Boreal summer intraseasonal oscillation (BSISO) is highly related to summer monsoon activities, tropical cyclones, flood disasters, and other extreme weather events in the Northern Hemisphere. The propagation of BSISO has considerable complexity. The apparent heat source (Q1) is the heat generated by radiation, heat conduction, and latent heat release, and their anomalies significantly affect the atmospheric circulation and relevant precipitation. We selected 27 significant events from 30- to 60-day Q1 anomalies in the northeast Arabian Sea (12–22° N, 66–76° E). K-means cluster analysis was used to further divide significant events into 19 Type-I events and 8 Type-II events. In the equatorial region, the Type-I events have continuous eastward propagation, while the Type-II events have no significant eastward propagation features before −10 days. In East Asia, the northward propagation of the Type-I events is significant and continuous, while there is no northward propagation of the Type-II events. The moisture analyses show that the horizontal advection term plays the most important role in the propagation of convection in most regions. The evaporation term of the Type-I events also plays a significant role in East Asia, and may be related to the difference between the two types of events there.