Aerosol Effects on Different Types of Clouds
Aerosol particles are the seeds of cloud droplets. Increases in droplet number concentration due to aerosol emissions by human activity can make clouds brighter by reducing droplet size (which increases surface area for the same droplet volume) and by inhibiting precipitation, which allows clouds to hold more liquid water. Climate models suggest the latter mechanism might be stronger for clouds that precipitate than those that do not. Recently, a team from Nanjing University, the DOE’s Pacific Northwest National Laboratory, and several other research organizations examined the effects of aerosol particles on various types of clouds simulated by a variety of global climate models. By separating their analysis into different cloud types, they identified quite different sensitivities of the cloud liquid water content to aerosols for shallow non-precipitating clouds and precipitating clouds. They found that aerosol effects on precipitating clouds contribute the most to the combined aerosol effects on the Earth’s energy balance. Previous field studies have focused on non-precipitating clouds, so this suggests a need to conduct field studies of aerosol effects on precipitating clouds. Most field studies of aerosol effects on clouds have focused on clouds that do not rain. This research suggests more attention should be devoted to aerosol effects on the liquid water content of precipitating clouds.
M. Wang acknowledged the support from the Jiangsu Province Specially-appointed professorship grant and the One Thousand Young Talents Program and the National Natural Science Foundation of China (41575073). The contribution from Pacific Northwest National Laboratory was supported by the US Department of Energy (DOE), Office of Science, Decadal and Regional Climate Prediction using Earth System Models (EaSM program). H. Wang acknowledges support by the DOE Earth System Modeling program. The Pacific Northwest National Laboratory is operated for the DOE by Battelle Memorial Institute under contract DE-AC06-76RLO 1830. The ECHAM-HAMMOZ model is developed by a consortium composed of ETH Zurich, Max Planck Institut für Meteorologie, Forschungszentrum Jülich, University of Oxford, the Finnish Meteorological Institute and the Leibniz Institute for Tropospheric Research, and managed by the Center for Climate Systems Modeling (C2SM) at ETH Zurich. D. Neubauer gratefully acknowledges the support by the Austrian Science Fund (FWF): J 3402-N29 (Erwin Schrödinger Fellowship Abroad). The Center for Climate Systems Modeling (C2SM) at ETH Zurich is acknowledged for providing technical and scientific support. This work was supported by a grant from the Swiss National Supercomputing Centre (CSCS) under project ID s431. D. G. Partridge would like to acknowledge support from the UK Natural Environment Research Council project ACID-PRUF (NE/I020148/1) as well as thanks to N. Bellouin for useful discussions during the course of this work. The development of GLOMAP-mode within HadGEM is part of the UKCA project, which is supported by both NERC and the Joint DECC/Defra Met Office Hadley Centre Climate Programme (GA01101). We acknowledge use of the MONSooN system, a collaborative facility supplied under the Joint Weather and Climate Research Programme, a strategic partnership between the Met Office and the Natural Environment Research Council. P. Stier would like to acknowledge support from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. FP7-280025.