El Niño–Southern Oscillation (ENSO) effect on interannual variability in spring aerosols over East Asia

Abstract

Abstract. Effects of the El Niño–Southern Oscillation (ENSO) on the interannual variability in spring aerosols over East Asia are investigated using the Modern Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) reanalysis aerosol data. Results show that the ENSO has a crucial effect on the spring aerosols over mainland South East Asia, southern China, and the ocean south of Japan. The above-normal (below-normal) aerosols are found over these regions during the ensuing spring of El Niño (La Niña). In contrast to the local aerosol diffusion in winter, the ENSO affects East Asian aerosols in the following spring mainly via the modulation of upstream aerosol generation and transport processes. The underlying physical mechanism is that during the ensuing spring of El Niño (La Niña), the dry (wet) air and reduced (enhanced) precipitation are beneficial for the increase (reduction) in biomass burning activities over northern mainland South East Asia, resulting in more (fewer) carbonaceous aerosol emissions. On the other hand, the anomalous anticyclone (cyclone) over the north-western Pacific (WNP) associated with El Niño (La Niña) enhances (weakens) the low-level south-westerly wind from northern mainland South East Asia to southern Japan, which transports more (less) carbonaceous aerosol downstream. Anomalous precipitation plays a role in reducing aerosols over the source region, but its washout effect over the downstream region is limited. The ENSO's impact on the ensuing spring aerosols is mainly attributed to the eastern Pacific ENSO rather than the central Pacific ENSO.