The sulfate‐CCN‐cloud albedo effect

Aerosol particles, such as sulfate aerosols, can act as cloud condensation nuclei (CCN). The CCN spectrum and the water vapour supply in a cloud determine the cloud droplet number concentration (CDNC) and hence the shortwave optical properties of low-level liquid clouds. The capability of anthropogenic aerosols to increase cloud reflectivity and thereby cool the Earth's surface is referred to as the indirect effect of anthropogenic aerosols. To obtain an estimate of this effect on climate, we empirically relate the CDNC, and thus the cloud optical properties, of two general circulation models (GCM) to the sulfate aerosol mass concentration derived from a chemical transport model. Based on a series of model experiments, the normalized globally averaged indirect forcing is about − 1 W/m 2 and ranges from – 0.5 to − 1.5 W/m 2 in both GCMs for different experiments. However, it is argued that the total uncertainty of the forcing is certainly larger than this range. The overall agreement between the two climate models is good, although the geographical distributions of the forcing are somewhat different. The highest forcings occur in and off the coasts of the polluted regions of the Northern Hemisphere. The regional distribution of the forcing and the land/sea contrast are very sensitive to the choice of the CDNC-sulfate mass relationship. The general patterns of the forcing, and the appropriateness of the different CDNC-sulfate mass relationships, are assessed. We also examine the simulated droplet effective radii and compare them with satellite retrievals. DOI: 10.1034/j.1600-0889.47.issue3.1.x

[1]  Peter V. Hobbs,et al.  Aerosol-cloud interactions , 1993 .

[2]  B. Rockel,et al.  A parameterization of broad band radiative transfer properties of water, ice, and mixed clouds , 1991 .

[3]  P. Hobbs,et al.  Comparisons of sulfate and nitrate production in clouds on the mid-Atlantic and Pacific Northwest Coasts of the United States , 1988 .

[4]  P. Hobbs,et al.  Reassessing the dependence of cloud condensation nucleus concentration on formation rate , 1994, Nature.

[5]  D. L. Roberts,et al.  A climate model study of indirect radiative forcing by anthropogenic sulphate aerosols , 1994, Nature.

[6]  S. Twomey.  Pollution and the Planetary Albedo , 1974 .

[7]  T. L. Wolfe,et al.  An assessment of the impact of pollution on global cloud albedo , 1984 .

[8]  Zhaoxin Li,et al.  Sensitivity of an atmospheric general circulation model to prescribed SST changes: feedback effects associated with the simulation of cloud optical properties , 1991 .

[9]  A. Lacis,et al.  Near-Global Survey of Effective Droplet Radii in Liquid Water Clouds Using ISCCP Data. , 1994 .

[10]  S. Twomey,et al.  Determining the Susceptibility of Cloud Albedo to Changes in Droplet Concentration with the Advanced Very High Resolution Radiometer , 1994 .

[11]  J. W. Fitzgerald,et al.  Aerosol size distributions and optical properties found in the marine boundary layer over the Atlantic Ocean , 1990 .

[12]  R. Charlson.  Gas-to-Particle Conversion and CCN Production , 1993 .

[13]  Robert J. Charlson,et al.  Perturbation of the northern hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols , 1991 .

[14]  D. Tanré,et al.  Effect of variations in super-saturation on the formation of cloud condensation nuclei , 1994, Nature.

[15]  R. Charlson,et al.  Cloud droplet number studies with a counterflow virtual impactor , 1994 .

[16]  D. Hegg.  Cloud condensation nucleus-sulphate mass relationship and cloud albedo , 1994 .

[17]  S. Twomey,et al.  The nuclei of natural cloud formation part II: The supersaturation in natural clouds and the variation of cloud droplet concentration , 1959 .

[18]  Yves Fouquart,et al.  Sulfur emission, CCN, clouds and climate : a review , 1992 .

[19]  J. Kiehl,et al.  The Relative Roles of Sulfate Aerosols and Greenhouse Gases in Climate Forcing , 1993, Science.

[20]  K. E. Taylor,et al.  Response of the climate system to atmospheric aerosols and greenhouse gases , 1994, Nature.

[21]  J. Penner,et al.  Quantifying and minimizing uncertainty of climate forcing by anthropogenic aerosols , 1994 .

[22]  R. Cess,et al.  Effect of anthropogenic sulfate aerosols on low-level cloud albedo over oceans , 1993 .

[23]  L. Radke,et al.  MEASUREMENTS OF THE SCAVENGING OF SULFATE AND NITRATE IN CLOUDS , 1984 .

[24]  B. Albrecht.  Aerosols, Cloud Microphysics, and Fractional Cloudiness , 1989, Science.

[25]  George A. Isaac,et al.  The relationship between cloud droplet number concentrations and anthropogenic pollution : observations and climatic implications , 1992 .

[26]  Paul G. Falkowski,et al.  Natural Versus Anthropogenic Factors Affecting Low-Level Cloud Albedo over the North Atlantic , 1992, Science.

[27]  Christine A. O'Neill,et al.  Effects of Aerosol from Biomass Burning on the Global Radiation Budget , 1992, Science.

[28]  A. Clarke.  Atmospheric nuclei in the remote free-troposphere , 1992 .

[29]  P. Quinn,et al.  Dimethylsulfide/cloud condensation nuclei/climate system - Relevant size-resolved measurements of the chemical and physical properties of atmospheric aerosol particles , 1993 .

[30]  T. Wigley,et al.  Possible climate change due to SO2-derived cloud condensation nuclei , 1989, Nature.

[31]  B. Hicks,et al.  Trends in global marine cloudiness and anthropogenic sulfur , 1994 .

[32]  J. Coakley,et al.  Climate Forcing by Anthropogenic Aerosols , 1992, Science.

[33]  R. Smith.  A scheme for predicting layer clouds and their water content in a general circulation model , 1990 .

[34]  Kuan-Man Xu,et al.  Evaluation of cloudiness parameterizations using a cumulus ensemble model , 1991 .

[35]  P. Crutzen,et al.  Anthropogenic influence on the distribution of tropospheric sulphate aerosol , 1992, Nature.

[36]  Michael D. King,et al.  Optical properties of marine stratocumulus clouds modified by ships , 1993 .

[37]  D. Covert,et al.  Atmospheric sulfur chemistry and cloud condensation nuclei (CCN) concentrations over the northeastern Pacific Coast , 1993 .

[38]  M. King,et al.  Direct and Remote Sensing Observations of the Effects of Ships on Clouds , 1989, Science.

[39]  G. M. Frick,et al.  Effect of nonprecipitating clouds on the aerosol size distribution in the marine boundary layer , 1986 .

[40]  S. Schwartz,et al.  EFFICIENT SCAVENGING OF AEROSOL SULFATE BY LIQUID-WATER CLOUDS* , 1987 .

[41]  J. Kristjánsson,et al.  Condensation and Cloud Parameterization Studies with a Mesoscale Numerical Weather Prediction Model , 1989 .

[42]  J. Houghton,et al.  Climate change 1992 : the supplementary report to the IPCC scientific assessment , 1992 .

[43]  Hilding Sundqvist,et al.  A parameterization scheme for non-convective condensation including prediction of cloud water content , 1978 .

[44]  J. Penner,et al.  Large contribution of organic aerosols to cloud-condensation-nuclei concentrations , 1993, Nature.

[45]  G. Isaac,et al.  On the relationship between sulfate and cloud droplet number concentrations , 1994 .

[46]  S. Schwartz.  Are global cloud albedo and climate controlled by marine phytoplankton? , 1988, Nature.

[47]  Henning Rodhe,et al.  A global three-dimensional model of the tropospheric sulfur cycle , 1991 .

[48]  R. Charlson,et al.  Sulphate aerosol and climate , 1990, Nature.

[49]  D. Hartmann.  Radiative effects of clouds on Earth's climate , 1993 .

[50]  Stephen Nicholls,et al.  Observations of marine stratocumulus clouds during FIRE , 1988 .

[51]  J. P. Taylor,et al.  Measurements of Cloud Susceptibility , 1994 .

[52]  H. Sievering,et al.  Cloud scavenging of aerosol sulfur: Two case studies , 1984 .

[53]  J. Coakley,et al.  Effect of Ship-Stack Effluents on Cloud Reflectivity , 1987, Science.

[54]  K. Noone,et al.  The influence of aerosol particle composition on cloud droplet formation , 1994 .