Vol.:(0123456789) 1 3 Climate Dynamics https://doi.org/10.1007/s00382-018-4267-3 Circulation responses to regional aerosol climate forcing in summer over East Asia Guoxing Chen 1  · Wei‑Chyung Wang 1  · Jen‑Ping Chen 2 Received: 11 November 2017 / Accepted: 10 May 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract For East Asia, circulation responses to anthropogenic aerosol radiative forcing dominate aerosol-precipitation interactions. To gain insights, this study analyzed CESM simulated circulation changes related to the ‘north drought and south food’ pattern caused by aerosol increases between two cases. One case was driven by the year-1850 global emission inventory, whereas the other used identical emissions for all regions except East Asia where anthropogenic emissions of aerosols and precursors of the year-2000 were imposed. Results show that the cooling caused by increased aerosols, which peaks at the middle latitudes, induces two intervened anomalous circulations in the troposphere. Near the surface, the increased land pressure weakens the southerlies and reduces the moisture transport for the entire eastern China. Meanwhile, in the free troposphere, the anomalous circulation exhibits remarkable meridional variations. While convergence occurs over 25°–45°N which partially compensates the decrease of moisture transport from lower levels, divergence develops over regions to the north which enhances the moisture defciency. In addition, the southward shift of the jet stream stimulates anomalous rising and sinking motions over the south and north of 32°N. The combination of these changes leads to precipitation increase in the Yangtze River Valley but decrease over North China. Keywords Aerosol climate forcing · East Asia · Summer monsoon · Jet stream 1 Introduction The East Asia climate, dominated by the monsoon circu- lation (Ding and Chan 2005), has undergone signifcant changes during the past few decades. One of the remarkable features is the ‘north drought and south food’ pattern, where the precipitation decreases over North China but increases over South China (especially the middle and lower parts of the Yangtze-Huai River Valley) (Gong and Ho 2002; Yu et al. 2004; Ren et al. 2005; Zhai et al. 2005; Yu and Zhou 2007; Zhou et al. 2009a). Besides natural factors (e.g., the phase shift of the Pacifc Decadal Oscillation; Zhou et al. 2008; Li et al. 2010), the rapidly increasing aerosol loading over this region has been identifed as a possible cause (Wu et al. 2015; Li et al. 2016). On the one hand, more aerosols lead to more but smaller cloud droplets, which may suppress the light precipitation and enhance the heavy precipitation (e.g., Rosenfeld et al. 2008); on the other hand, increasing aerosols change the radiation budget via aerosol-radiation and aerosol-cloud-radiation interactions and thus modify the atmospheric stability on local or continental scales, which subsequently alters the circulation and redistributes the pre- cipitation in time and space (e.g., Ramanathan et al. 2001; Yang et al. 2013a, b). While the former has been gener- ally accepted by the community, the latter is still disputable and not adequately addressed in previous studies. Detailed explanations of the mechanism and particularly its associa- tions with regional precipitation changes are still lacking. This paper is a contribution to the special issue on East Asian Climate under Global Warming: Understanding and Projection, consisting of papers from the East Asian Climate (EAC) community and the 13th EAC International Workshop in Beijing, China on 24-25 March 2016, and coordinated by Jianping Li, Huang-Hsiung Hsu, Wei-Chyung Wang, Kyung-Ja Ha, Tim Li, and Akio Kitoh. * Guoxing Chen gchen4@albany.edu 1 Atmospheric Sciences Research Center, University at Albany, State University of New York, Albany, NY 12203, USA 2 Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan