Asymmetric Responses of Precipitation over the Maritime Continent in the ENSO events

Abstract:

The Maritime Continent (MC) has one of the largest regional rainfall rates in the world, and through strong convective heating, the MC plays an important role in the Earth’s energy balance and hydrological cycle. During El Nino, the warm pool moves to the east so that convection and precipitation over the MC decreases; in contrast, more active convection and precipitation occurs in the region during La Nina. In this study, we used global precipitation data sets including TRMM and GPCP to demonstrate that precipitation in the MC has an asymmetric response over the land and nearby oceans during different phases of ENSO. Using Ocean Nino Index as a metric for ENSO strength, we show that El Nino significantly reduces precipitation in Celebes Sea and the oceanic regions between Koror and Papua Barat, but causes significantly smaller reductions in nearby islands including Papua and Borneo. The cloud amount decreases over the MC during the El Nino, which may lead to increases in incoming solar radiation. Greater land heating rates, in turn, may enhance land-sea breezes, causing greater precipitation on these islands than in nearby ocean areas. In addition, evapotranspiration over the islands might mitigate the precipitation changes over the land, making precipitation over land less variable during El Nino. Further investigation and model experiments are needed to explore what kinds of mechanisms dominate such asymmetric precipitation responses over the MC.