Impacts of recent decadal changes in Asian aerosols on the East Asian summer monsoon: roles of aerosol–radiation and aerosol–cloud interactions

Abstract

Anthropogenic aerosols (AA) can affect cloud and precipitation through aerosol-radiation interaction (ARI) and aerosolcloud interaction (ACI). Over the past few decades, anthropogenic aerosol emissions have exhibited remarkable changes in the magnitude and in spatial pattern. The most significant changes are the increased emissions over both South Asia and East Asia. In this study, the atmospheric component of a state-of-the-art climate model that includes eight species of tropospheric aerosols, coupled to a multi-level mixed-layer ocean model, has been used to investigate the impacts of Asian anthropogenic aerosol precursor emission changes from 1970s to 2000s on large scale circulation and precipitation in boreal summer over East Asia. Results reveal significant changes in circulation and clouds over East Asia and over the tropical and western North Pacific (WNP). Increased Asian AA emissions lead to anomalous cyclonic circulation over the Maritime continent (MC) and anomalous anticyclonic circulation over the WNP, resulting in anomalous moisture transport convergence over the MC and therefore increased precipitation. They also lead to anomalous moisture flux divergence over both the WNP and large land areas of East Asia, especially over northern China, and therefore decreased precipitation there. These large scale circulation anomalies over the adjacent oceans are related to aerosol change induced ocean feedbacks, predominantly through ACI. It is the slow responses over the adjacent oceans (e.g., SST changes) through coupled atmosphere-ocean interaction in pre-monsoon seasons and summer that shape the changes of the East Asian summer monsoon and local precipitation. The results in this study suggest that increased Asian AA emissions from 1970s to 2000s may have played an important role for the observed southward shift of the Pacific intertropical convergence zone and precipitation belt, weakening of East Asian summer monsoon and reduced precipitation over northern China in East Asia during the latter half of the twentieth century.

Projected near-term changes of temperature extremes in Europe and China under different aerosol emissions

“…This increase in water vapor is likely to be associated with the strengthened East Asian summer monsoon (EASM) with southwesterly and southerly anomalies along the coast of East China through enhanced land sea warming contrast (figures S12(c), (d) and 6(b)). The EASM response to the AA forcing is in agreement with previous results (Tian et al 2018, Dong et al 2019. Interestingly, there is a relatively weak and insignificant warming over North China ( figure 6(b)), which is reflected in the changes in TXx and summer Tmax (figures 4(a) and 5(b)).…”

Northern Hemisphere Land Monsoon Precipitation Increased by the Green Sahara During Middle Holocene

“…Understanding the dynamics of Northern Hemisphere land monsoon (NHLM) and reliably projecting its future changes are vitally important for infrastructure planning, disaster mitigation, food security, and water resource management (Wang et al, ; Wang et al, ). The changes in NHLM precipitation (NHLMP, defined in section ) are driven by natural (Liu et al, ; Stevenson et al, ; Sun et al, ; Sun et al, ) and anthropogenic forcings (Devaraju et al, ; Dong et al, ; Giannini & Kaplan, ; Lau et al, ; Vecchi et al, ) through the global sea surface temperature (SST) changes (Giannini et al, ) and are also affected by the low‐frequency internal modes within the earth's climate system (Wang et al, ; Wang et al, ). Observations show that NHLMP intensified over the past three decades (Wang et al, ) due to both internal variability and the effects of climate change.…”

Mechanisms for a remote response to Asian anthropogenic aerosol in boreal winter

“…Similarly, there is still debate about whether the climate response to increases in anthropogenic aerosols is a simple mirror of the response to increasing greenhouse gases (e.g. Feichter et al, 2004;Xie et al, 2013;Gillett et al, 2013).…”