Energetic Constraints on Seasonal Zonal Shifts of Indo-Pacific Intense Precipitation Regions

Peak Indo-Pacific precipitation shifts seasonally from the South Equatorial Western Pacific during boreal winter to the Bay of Bengal during boreal summer. Studies have shown that intense precipitation regions at seasonal timescale can be observed surrounding the crossing of the Energy Flux Equator (EFE) and Energy Flux Prime Meridian (EFPM) often referred to as the minima of Energy Flux Potential (EFP-min). To understand the seasonal zonal shifts of intense precipitation regions, we study the positions of EFP-min at monthly timescales. The climatological seasonal cycle of the EFP-min shows that from October to April, it resides over the West-Central Pacific, and from May to September, it stays over the East-Asian region. It never resides over the Maritime Continent Zone indicating a sudden jump from April to May and again from September to October. The reason behind these two energetic regimes is explained using an energy flux potential approach. It is found that from October to April, the meridional average surface turbulent heat flux potential alone makes EFP-min favorable to stay over the West-Central Pacific region. However, from May to September, the strength of the meridional average surface turbulent heat flux potential and radiative heat flux potential creates a condition for the EFP-min to stay over the East-Asian region. Further analyses show that the point of precipitation maxima follows EFP-min during the transition from boreal winter to boreal summer. However, it shows a three-month lag during the transition from boreal summer to winter. This lag might be attributed to the weak radiative heat flux over the tropical Western Pacific as compared to the Eastern Indian Ocean.