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.
Highlights
East Asia, especially China, has suffered heavy air pollution from various emission sources in recent decades (e.g. Streets and Waldhoff, 2000; Chan and Yao, 2008; Tao et al, 2017)
This study aims to address the following questions using long-term reanalysis aerosol data: (1) what are the impacts of El Niño–Southern Oscillation (ENSO) on the temporal and spatial distribution of ensuing spring aerosols over East Asia, and (2) what are the physical processes and relative roles of anomalous circulation and rainfall in altering ensuing spring aerosols over the region? This study differs from previous studies by focusing on the influence of ENSO on interannual variation in East Asian aerosols in spring based on the longterm observational data and on different mechanisms in winter and ensuing spring
We investigate the effects of ENSO on the ensuing spring aerosols over East Asia based on the National Aeronautics and Space Administration (NASA) MERRA-2 aerosol reanalysis data during 1980–2019; we discuss different effects of the two ENSO types
Summary
East Asia, especially China, has suffered heavy air pollution from various emission sources in recent decades (e.g. Streets and Waldhoff, 2000; Chan and Yao, 2008; Tao et al, 2017). Feng et al (2017) found an anomalous dipole pattern of aerosol concentrations over eastern China (i.e. increased aerosols in the south and reduced aerosols in the north) during the mature phase of the strong ENSO event of 1998/1999, while this dipole pattern was reversed during the moderate event of 2000/2001 Most of these studies only focused on the winter season (Gao and Li, 2015; Sun et al, 2018; Zhao et al, 2018; Yu et al, 2019), and some discrepancies exist among these results; e.g. the regions with significant aerosol changes are different between the findings of Sun et al (2018) and Zhao et al (2018).
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