Anthropogenic Aerosols Significantly Reduce Mesoscale Convective System Occurrences and Precipitation Over Southern China in April

• Published in: Geophysical research letters 2020-03, Vol.47 (6), p.n/a
• Main Authors: Zhang, Lijuan, Fu, Tzung‐May, Tian, Heng, Ma, Yaping, Chen, Jen‐Ping, Tsai, Tzu‐Chin, Tsai, I‐Chun, Meng, Zhiyong, Yang, Xin
• Format: Article
• Language: English
• Subjects: Aerosol effects; Aerosols; aerosol‐cloud interactions; aerosol‐radiation interactions; Air pollution; anthropogenic aerosols; Anthropogenic factors; Atmosphere; Atmospheric precipitations; Clouds; Computer simulation; Human influences; Lower atmosphere; Mesoscale convective systems; Precipitation; Rain; Rainfall; Reduction; Reflectance; Scattering
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL086204

Precipitation over Southern China in April, largely associated with mesoscale convective systems (MCSs), has declined significantly in recent decades. It is unclear how this decline in precipitation may be related to the concurrent increase of anthropogenic aerosols over this region. Here, using observation analyses and model simulations, we showed that increased levels of anthropogenic aerosols can significantly reduce MCS occurrences by 21% to 32% over Southern China in April, leading to less rainfall. Half of this MCS occurrence reduction was due to the direct radiative scattering of aerosols and the indirect enhancement of non‐MCS liquid cloud reflectance by aerosols, which stabilized the regional atmosphere. The other half of the MCS occurrence reduction was due to the microphysical and dynamical responses of the MCS to aerosols. Our results demonstrated the complex effects of aerosols on MCSs via impacts on both the convective systems and on the regional atmosphere. Plain Language Summary Rainfall over Southern China for the month of April has decreased significantly between the late 1970s and the late 2000s, concurrent with increasing anthropogenic aerosol pollution in this region. Through model simulations, we found that higher levels of aerosols and the resulting increase in liquid cloud reflectance both enhanced the scattering of sunlight, cooled the surface, and stabilized the lower atmosphere. As a result, the occurrences of strong, well‐organized convective systems were suppressed, leading to decreased rainfall over Southern China in April. Key Points Anthropogenic aerosols inhibit mesoscale convective systems and reduce convective precipitation over Southern China in April Aerosols directly scatter solar radiation and indirectly exert Twomey effect on warm clouds to stabilize regional atmosphere