Response of the link between ENSO and the East Asian winter monsoon to Asian anthropogenic aerosols

Abstract. We use coupled and atmosphere-only simulations from the Precipitation Driver and Response Model Intercomparison Project to investigate the impacts of Asian anthropogenic sulfate aerosols on the link between the El Niño-Southern Oscillation (ENSO) and the East Asian Winter monsoon (EAWM). In fully-coupled simulations, aerosol-induced cooling extends southeastward to the Maritime Continent and the north-western Pacific. Remotely, this broad cooling weakens the easterly trade winds over the central Pacific, which reduces the east-west equatorial Pacific sea surface temperature gradient. These changes contribute to increasing ENSO's amplitude by 17 %, mainly through strengthening the zonal wind forcing. Concurrently, the El Niño-related warm SST anomalies and the ensuing Pacific-East Asia teleconnection pattern (i.e. the ENSO-EAWM link) intensify, leading to an increased EAWM amplitude by 18 % in the coupled simulations. Therefore, in response to the increasing frequency of El Niño and La Niña years under Asian aerosol forcing, the interannual variability of the EAWM increases, with more extreme EAWM years. The opposite variations in the interannual variability of the EAWM to Asian aerosols in atmosphere-only simulations (−19 %) further reflect the importance of ENSO-related atmosphere-ocean coupled processes. A better understanding of the changes of the year-to-year variability of the EAWM in response to aerosol forcing is critical to reducing uncertainties in future projections of variability of regional extremes, such as cold surges and flooding, which can cause large social and economic impacts on densely populated East Asia.