Sensitivity study of cloud parameterizations with relative dispersion in CAM5.1: impacts on aerosol indirect effects

Abstract. Aerosol-induced increase of relative dispersion of cloud droplet size distribution e exerts a warming effect and partly offsets the cooling of aerosol indirect radiative forcing (AIF) associated with increased droplet concentration by increasing the cloud droplet effective radius (Re) and enhancing the cloud-to-rain autoconversion rate (Au) (labeled as the dispersion effect), which can help reconcile global climate models (GCMs) with the satellite observations. However, the total dispersion effects on both Re and Au are not fully considered in most GCMs, especially in different versions of the Community Atmospheric Model (CAM). In order to accurately evaluate the dispersion effect on AIF, the new complete cloud parameterizations of Re and Au explicitly accounting for e are implemented into the CAM version 5.1 (CAM5.1), and a suite of sensitivity experiments is conducted with different representations of e reported in the literature. It is shown that the shortwave cloud radiative forcing is much better simulated with the new cloud parameterizations as compared to the standard scheme in CAM5.1, whereas the influences on longwave cloud radiative forcing and surface precipitation are minimal. Additionally, consideration of the dispersion effect can significantly reduce the changes induced by anthropogenic aerosols in the cloud-top effective radius and the liquid water path, especially in the Northern Hemisphere. The corresponding AIF with the dispersion effect considered can also be reduced substantially by a range of 0.10 to 0.21 W m−2 at the global scale and by a much bigger margin of 0.25 to 0.39 W m−2 for the Northern Hemisphere in comparison with that of fixed relative dispersion, mainly dependent on the change of relative dispersion and droplet concentrations (Δe∕ΔNc).

[1]  J. Janowiak,et al.  The Version 2 Global Precipitation Climatology Project (GPCP) Monthly Precipitation Analysis (1979-Present) , 2003 .

[2]  U. Lohmann,et al.  Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM , 2007 .

[3]  Aircraft measurements of cloud droplet spectral dispersion and implications for indirect aerosol radiative forcing , 2006 .

[4]  Leon D. Rotstayn,et al.  Sensitivity of the first indirect aerosol effect to an increase of cloud droplet spectral dispersion with droplet number concentration , 2003 .

[5]  W. Rossow,et al.  Advances in understanding clouds from ISCCP , 1999 .

[6]  T. Takemura,et al.  Evaluation of autoconversion schemes in a single model framework with satellite observations: EVALUATION OF AUTOCONVERSION SCHEMES , 2015 .

[7]  P. Daum,et al.  Analytical expression for the relative dispersion of the cloud droplet size distribution , 2006 .

[8]  P. Daum,et al.  Anthropogenic aerosols: Indirect warming effect from dispersion forcing , 2002, Nature.

[9]  W. Paul Menzel,et al.  The MODIS cloud products: algorithms and examples from Terra , 2003, IEEE Trans. Geosci. Remote. Sens..

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

[11]  D. W. Johnson,et al.  The Measurement and Parameterization of Effective Radius of Droplets in Warm Stratocumulus Clouds , 1994 .

[12]  Yu Liu,et al.  A method for solving relative dispersion of the cloud droplet spectra , 2015, Science China Earth Sciences.

[13]  U. Lohmann,et al.  Influence of Giant CCN on warm rain processes in the ECHAM5 GCM , 2007 .

[14]  Xiao-dong Liu,et al.  Aerosol-cloud-precipitation interactions in WRF model: Sensitivity to autoconversion parameterization , 2015, Journal of Meteorological Research.

[15]  Johannes Quaas,et al.  Model intercomparison of indirect aerosol effects , 2006 .

[16]  Jiwen Fan,et al.  Improving bulk microphysics parameterizations in simulations of aerosol effects , 2013 .

[17]  Andrew Gettelman,et al.  Advanced Two-Moment Bulk Microphysics for Global Models. Part II: Global Model Solutions and Aerosol–Cloud Interactions* , 2015 .

[18]  S. Klein,et al.  Global simulations of ice nucleation and ice supersaturation with an improved cloud scheme in the Community Atmosphere Model , 2010 .

[19]  Yiran Peng,et al.  Dispersion bias, dispersion effect, and the aerosol–cloud conundrum , 2008 .

[20]  Andrew Gettelman,et al.  A new two-moment bulk stratiform cloud microphysics scheme in the Community Atmosphere Model, version 3 (CAM3). Part I: Description and numerical tests , 2008 .

[21]  U. Lohmann,et al.  An investigation into the aerosol dispersion effect through the activation process in marine stratus clouds , 2007 .

[22]  T. Takemura,et al.  Evaluation of autoconversion schemes in a single model framework with satellite observations , 2015 .

[23]  Leon D. Rotstayn,et al.  Cloud droplet spectral dispersion and the indirect aerosol effect: Comparison of two treatments in a GCM , 2009 .

[24]  Philip J. Rasch,et al.  Toward a Minimal Representation of Aerosols in Climate Models: Comparative Decomposition of Aerosol Direct, Semidirect, and Indirect Radiative Forcing , 2012 .

[25]  Yangang Liu,et al.  Parameterization of the Autoconversion Process. Part I: Analytical Formulation of the Kessler-Type Parameterizations , 2004 .

[26]  R. Welch,et al.  Global variation of column droplet concentration in low‐level clouds , 1998 .

[27]  W. Paul Menzel,et al.  Cloud and aerosol properties, precipitable water, and profiles of temperature and water vapor from MODIS , 2003, IEEE Trans. Geosci. Remote. Sens..

[28]  David S. Lee,et al.  Historical (1850–2000) gridded anthropogenic and biomass burning emissions of reactive gases and aerosols: methodology and application , 2010 .

[29]  Yiran Peng,et al.  Numerical simulation of clouds and precipitation depending on different relationships between aerosol and cloud droplet spectral dispersion , 2013 .

[30]  S. Ghan.  Technical Note: Estimating aerosol effects on cloud radiative forcing , 2013 .

[31]  W. Collins,et al.  Radiative forcing by long‐lived greenhouse gases: Calculations with the AER radiative transfer models , 2008 .

[32]  W. Collins,et al.  Geoscientific Model Development Toward a minimal representation of aerosols in climate models : description and evaluation in the Community Atmosphere Model CAM 5 , 2012 .

[33]  U. Lohmann,et al.  Global indirect aerosol effects: a review , 2004 .

[34]  Robert Wood,et al.  Drizzle in Stratiform Boundary Layer Clouds. Part II: Microphysical Aspects. , 2005 .

[35]  D. Jackson,et al.  Trends in Global Cloud Cover in Two Decades of HIRS Observations , 2005 .

[36]  C. Chuang,et al.  Sensitivity of aerosol indirect effects to cloud nucleation and autoconversion parameterizations in short‐range weather forecasts during the May 2003 aerosol IOP , 2012 .

[37]  Andrew Gettelman,et al.  A new two-moment bulk stratiform cloud microphysics scheme in the NCAR Community Atmosphere Model (CAM3), Part II: Single-Column and Global Results , 2007 .

[38]  David R. Doelling,et al.  Toward Optimal Closure of the Earth's Top-of-Atmosphere Radiation Budget , 2009 .

[39]  S. Solomon.  The Physical Science Basis : Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007 .

[40]  W. Collins,et al.  Description of the NCAR Community Atmosphere Model (CAM 3.0) , 2004 .

[41]  J. Penner,et al.  Does the threshold representation associated with the autoconversion process matter , 2007 .

[42]  M. Miller,et al.  Theoretical expression for the autoconversion rate of the cloud droplet number concentration , 2007 .

[43]  Leon D. Rotstayn,et al.  A smaller global estimate of the second indirect aerosol effect , 2005 .

[44]  W. Collins,et al.  An AeroCom Initial Assessment - Optical Properties in Aerosol Component Modules of Global Models , 2005 .

[45]  U. Lohmann,et al.  Sensitivity study of the spectral dispersion of the cloud droplet size distribution on the indirect aerosol effect , 2003 .

[46]  P. Daum,et al.  Spectral dispersion of cloud droplet size distributions and the parameterization of cloud droplet effective radius , 2000 .

[47]  Xiao-dong Liu,et al.  Analytical three-moment autoconversion parameterization based on generalized gamma distribution , 2009 .

[48]  M. Khairoutdinov,et al.  A New Cloud Physics Parameterization in a Large-Eddy Simulation Model of Marine Stratocumulus , 2000 .

[49]  S. Twomey.  The Influence of Pollution on the Shortwave Albedo of Clouds , 1977 .

[50]  V. Ramanathan,et al.  Aerosols, Climate, and the Hydrological Cycle , 2001, Science.

[51]  Robert Wood.  Parametrization of the effect of drizzle upon the droplet effective radius in stratocumulus clouds , 2000 .

[52]  H. Morrison,et al.  Comparison of Bulk and Bin Warm-Rain Microphysics Models Using a Kinematic Framework , 2007 .

[53]  Y. Wang,et al.  Implementation of a two‐moment bulk microphysics scheme to the WRF model to investigate aerosol‐cloud interaction , 2008 .