Different impacts of two types of Pacific Ocean warming on Southeast Asian rainfall during boreal winter

The impacts of conventional El Nino-Southern Oscillation (ENSO) and ENSO Modoki on wintertime Southeast Asian rainfall and related mechanisms are studied using the method of partial regression and correlation and numerical simulations of a simple baroclinic model. Results show that the Southeast Asian rainfall associated with these two kinds of ENSO exhibits different spatial distributions. In the case of El Nino, wet conditions are observed over south China, and dry conditions are seen over the Philippines, Borneo, Celebes, and Sulawesi. In contrast, for El Nino Modoki, the negative rainfall anomalies around the Philippines are weaker and are located more northward compared to the El Nino counterpart. The different Southeast Asian rainfalls that are related to ENSO and ENSO Modoki are attributed to the different anomalous Walker circulation and low-level anticyclone around the Philippines. Both the Philippine anticyclone and the descending branch center of the Walker circulation over the western North Pacific occupy a smaller domain and are located more northward during El Nino Modoki than during El Nino. All of these factors favor the difference in the Southeast Asian rainfall anomalies between the two events. Numerical experiments also suggest that the different low-level atmospheric responses are mainly induced by different diabatic cooling over the western North Pacific related to El Nino and El Nino Modoki.