Multi-sensor quantification of aerosol-induced variability in warm clouds over eastern China Fu Wang a, b , Jianping Guo b, * , Jiahua Zhang c , Jingfeng Huang d , Min Min e , Tianmeng Chen f , Huan Liu b , Minjun Deng b , Xiaowen Li g a School of Resources and Environment, University of Electronic Science and Technology of China, Chengdu 610054, China b Institute of Atmosphere Composition, Chinese Academy of Meteorological Sciences, Beijing 100081, China c Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China d ESSIC, University of Maryland, College Park, MD, USA e National Satellite Meteorological Center, Beijing 100081, China f CGCESS, Beijing Normal University, Beijing 100871, China g School of Geography, Beijing Normal University, Beijing 100871, China highlights  Aerosol-warm cloud interaction in eastern China is examined using multi-sensors.  The aerosol-cloud mixing state is identified by vertical aerosol and cloud layers.  Aerosol-cloud interaction strength is investigated during summer- and winter-season.  Cloud droplet radii response to aerosol follows a boomerang shape for mixed cases.  No apparent change in cloud droplet radii with AOD can be found for separated cases. article info Article history: Received 7 January 2015 Received in revised form 25 April 2015 Accepted 29 April 2015 Available online 30 April 2015 Keywords: Aerosol Caliop Aerosol indirect effect Mixing state abstract Aerosol-cloud (AC) interactions remain uncharacterized due to difficulties in obtaining accurate aerosol and cloud observations. In this study, we quantified the aerosol indirect effects (AIE) on warm clouds over Eastern China based on near-simultaneous retrievals from MODIS/AQUA, CALIOP/CALIPSO, and CPR/ CLOUDSAT between June 2006 and December 2010. The seasonality of aerosols from ground-based PM 10 (aerosol particles with diameter of 10 mm or less) significantly differed from that estimated using MODIS aerosol optical depth (AOD). This result was supported by the lower level frequency profile of aerosol occurrence from CALIOP, indicative of the significant role of CALIOP in the AC interaction. To focus on warm clouds, cloud layers with base (top) altitudes above 7 (10) km were excluded. The combination of CALIOP and CPR was applied to determine the exact position of warm clouds relative to aerosols out of the following six scenarios in terms of AC mixing states: 1) aerosol only (AO); 2) cloud only (CO); 3) single aerosol layer-single cloud layer (SASC); 4) single aerosol layer-double cloud layers (SADC); 5) double aerosol layers - single cloud layer (DASC); and 6) others. The cases with vertical distance between aerosol and cloud layer less (more) than 100 m (700 m) were marked mixed (separated), and the rest as uncertain. Results showed that only 8.95% (7.53%) belonged to the mixed (separated and uncertain) state among all of the collocated AC overlapping cases, including SASC, SADC, and DASC. Under mixed con- ditions, the cloud droplet effective radius (CDR) decreased with increasing AOD at moderate aerosol loading (AOD<0.4), and then became saturated at an AOD of around 0.5, followed by an increase in CDR with increasing AOD, known as boomerang shape. Under separated conditions, no apparent changes in CDR with AOD were observed. We categorized the AC dataset into summer- and winter-season subsets to determine how the boomerang shape varied with season. The response of CDR to AOD in summer exhibited similar but much more deepened boomerang shape, as compared with the all year round case. * Corresponding author. E-mail address: jpguo@cams.cma.gov.cn (J. Guo). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv http://dx.doi.org/10.1016/j.atmosenv.2015.04.063 1352-2310/© 2015 Elsevier Ltd. All rights reserved. Atmospheric Environment 113 (2015) 1e9