On Nov 5, 2021, Nature Communication published a paper titled “Aerosol-boundary-layer-monsoon interactions amplify semi-direct effect of biomass smoke on low cloud formation in Southeast Asia” by Professor Aijun Ding and his group and Max Planck Institute for Chemistry, Mainz, Germany. Based on systematic data analysis and numerical model simulation, the authors show that biomass burning aerosols aloft strongly increase the low cloud coverage in subtropical southeastern Asia. A synergetic effect of aerosol-cloud-boundary layer interaction with the monsoon is the main reason for the strong semi-direct effect and enhanced low cloud formation in southeastern Asia.

The authors adopted an Observation minus reanalysis (OMR) approach, combining MODIS satellite observational data with ECMWF (European Centre for Medium-Range Weather Forecast) Interim Re-Analysis (ERA-Interim) data. Simulations reproduce the effect of biomass-burning (BB) emission and aerosol optical depth (AOD) on the springtime low-cloud enhancement in southeastern Asia. Although the total BB emission in southeastern Asia in March–April, predominately from forest and agricultural fires in the northern Indochina Peninsula, is only 20% of that in southern Africa in June–August, the cloud cover in the main transport pathways of the smoke shows a similar enhancement (over 30%) in both cases (Fig. 1a, b). As demonstrated in Fig. 2, the averaged vertical distribution of CALIPSO aerosol extinction and cloud occurrence for high and low-AOD years also suggest a stronger vertical linkage of smoke aloft and low-cloud enhancement below in Asia. The authors conducted another WRF-Chem experiment (Weather Research and Forecasting model coupled with Chemistry) in the work and two feedback mechanisms impacting the process were reproduced: a. aerosol-cloud-radiation interaction coupling with PBL (planetary boundary layer) in the vertical direction. b. horizontal moisture supply under the influence of monsoon circulation adjusted by aerosol-radiation interaction (Fig.3).

Fig. 1: Observation minus reanalysis (OMR) difference in cloud fraction and its relationship to aerosol optical depth (AOD).

Fig. 2: Relationship between smoke and cloud occurrences measured by the CALIPSO satellite instruments.

Fig. 3: Synergetic feedback of smoke aerosol–cloud–boundary-layer interaction coupling with the monsoon in subtropical southeastern Asia.

Research Scientist Ke Ding and Associate Professor Xin Huang are the first authors of this paper. Professor Aijun Ding and Yafang Cheng from Max Planck Institute for Chemistry, Mainz, Germany are the co-corresponding authors. More than 20 scientists at home and abroad involved in the research. The work is financially supported by National Natural Science Foundation of China (41725020 and 41922038) and the CSC-China Scholarship Council for joint Ph.D. grant awarded to K.D, Collaborative Innovation Center for Climate Change and Frontiers Science Center for Critical Earth Material Cycling (FSC-CEMaC).

Article link: Ding, K., Huang, X., Ding, A. et al. Aerosol-boundary-layer-monsoon interactions amplify semi-direct effect of biomass smoke on low cloud formation in Southeast Asia. Nature Communications 12, 6416 (2021).