Interdecadal Variation of the Wintertime Precipitation in Southeast Asia and Its Possible Causes

Abstract

Based on several observational and reanalysis datasets for the winters 1901-2017, this study investigates the interdecadal (ID) variation of the Southeast Asian rainfall (SEAR) and its potential drivers. The dominant mode of the wintertime SEAR on the ID timescale features enhanced precipitation over the eastern Maritime Continent and the Philippines and a slight decrease of precipitation over the western Maritime Continent, or the opposite sign. The ID SEAR variability peaks at the 8-16-year period and explains more than 20% of the total variance regardless of the datasets and period considered, highlighting the importance of the ID variability of the SEAR. The atmospheric circulation that facilitates abundant ID SEAR is characterized by enhanced lower-tropospheric wind convergence and cyclonic anomalies over the South China Sea and the Philippines. On the one hand, this wind convergence is attributed to the enhanced Walker circulation induced by the negative phase of the Interdecadal Pacific Oscillation (IPO). On the other hand, it is attributed to the enhanced northerly anomalies along the coast of East Asia induced by strong East Asian winter monsoon (EAWM) and reduced autumn Arctic sea ice in the Barents-Kara Sea. These mechanisms are further confirmed by model experiments from the Coupled Model Intercomparison Project Phase 5. The effects of the IPO, EAWM, and Arctic sea ice on the SEAR are mostly independent. They together explain approximately 70% of the SEAR variance on the ID timescale. Based on several observational and reanalysis datasets for the winters 1901-2017, this study investigates the interdecadal (ID) variation of the Southeast Asian rainfall (SEAR) and its potential drivers. The dominant mode of the wintertime SEAR on the ID timescale features enhanced precipitation over the eastern Maritime Continent and the Philippines and a slight decrease of precipitation over the western Maritime Continent, or the opposite sign. The ID SEAR variability peaks at the 8-16-year period and explains more than 20% of the total variance regardless of the datasets and period considered, highlighting the importance of the ID variability of the SEAR. The atmospheric circulation that facilitates abundant ID SEAR is characterized by enhanced lower-tropospheric wind convergence and cyclonic anomalies over the South China Sea and the Philippines. On the one hand, this wind convergence is attributed to the enhanced Walker circulation induced by the negative phase of the Interdecadal Pacific Oscillation (IPO). On the other hand, it is attributed to the enhanced northerly anomalies along the coast of East Asia induced by strong East Asian winter monsoon (EAWM) and reduced autumn Arctic sea ice in the Barents-Kara Sea. These mechanisms are further confirmed by model experiments from the Coupled Model Intercomparison Project Phase 5. The effects of the IPO, EAWM, and Arctic sea ice on the SEAR are mostly independent. They together explain approximately 70% of the SEAR variance on the ID timescale.