Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 6 2009 10.5194/acpd-9-24717-2009 http://www.atmos-chem-phys-discuss.net/9/24717/2009/ http://www.atmos-chem-phys-discuss.net/9/24717/2009/acpd-9-24717-2009.html http://www.atmos-chem-phys-discuss.net/9/24717/2009/acpd-9-24717-2009.pdf 24717 24730 2009-11-18 Comprehensively accounting for the effect of giant CCN in cloud droplet activation parameterizations D. Barahona R. E. L. West P. Stier S. Romakkaniemi H. Kokkola A. Nenes athanasios.nenes@gatech.edu School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, USA School of Earth and Atmospheric Sciences, Georgia Institute of Technology, USA Atmospheric, Oceanic and Planetary Physics, Department of Physics, University\newline of Oxford, UK Department of Physics, University of Kuopio, Finland Finnish Meteorological Institute, Kuopio Unit, Finland Cloud droplet activation parameterizations used in aerosol indirect effect assessments often assume that droplet growth after activation is much greater than their equilibrium size close to cloud base. This assumption does not hold for large CCN which may experience limited growth. If a large fraction of the aerosol is composed of such particles (such as regions with large fractions of dust particles and seasalt), neglecting such kinetic limitations in cloud droplet activation parameterizations leads to an underestimation of droplet surface area during cloud formation, hence overestimation of maximum supersaturation and cloud droplet number. Here we present a simple approach to address this problem and that can easily be incorporated into cloud droplet activation parameterizations. A demonstration of this method is done for activation parameterizations based on the ''population splitting'' concept of Nenes and Seinfeld (2003). Abdul-Razzak,~H. and Ghan,~S.: A~parameterization of aerosol activation, 2. Multiple aerosol types, J. Geophys. Res., 105, 6837–6844, \doi6810.1029/1999JD901161, 2000. Barahona,~D. and Nenes,~A.: Parameterization of cloud droplet formation in large scale models: including effects of entrainment, J. Geophys. Res., J. Geophys. Res., 112, D16206, doi:10.1029/2007JD008473, 2007. Charlson,~R J., Seinfeld,~J H., Nenes,~A., Kulmala,~M., Laaksonen,~A., and Facchini,~M C.: Reshaping the theory of cloud formation, Science, 292, 2025–2026, 2001. Chuang,~P Y., Charlson,~R J., and Seinfeld,~J H.: Kinetic limitations on droplet formation in clouds, Nature, 390, 594–596, 1997. Cohard,~J.-M., Pinty,~J.-P., and Suhre,~K.: On the parameterization of activation spectra from cloud condensation nuclei microphysical properties, J. Geophys. Res., 105, 11753–11766, \doi11710.11029/11999JD901195, 2000. Feingold,~G. and Heymsfield,~A J.: Parameterization of condensational growth of droplets for use in general circulation models, J. Atmos. Sci., 49, 2325–2342, 1992. Fountoukis,~C. and Nenes,~A.: Continued development of a~cloud droplet formation parameterization for global climate models, J. Geophys. Res., 110, D11212, \doi11210.11029/12004JD005591, 2005. Kumar, P., Sokolik, I. N., and Nenes, A.: Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN, Atmos. Chem. Phys., 9, 2517–2532, 2009. Ming,~Y., Ramaswamy,~V., Donner,~L J., and Phillips,~V T J.: A~new parameterization of cloud droplet activation applicable to general circulation models, J. Atmos. Sci., 63, 1348–1356, 2006. Morrison,~H. and Grabowski,~W.: Modeling supersaturation and subgrid-scale mixing with two-moment bulk warm microphysics, J. Atmos. Sci., 65, 792–812, 2008. Nenes,~A., Ghan,~S., Abdul-Razzak,~H., Chuang,~P Y., and Seinfeld,~J H.: Kinetic limitations on cloud droplet formation and impact on cloud albedo, Tellus, 53B, 133–149, 2001. Nenes,~A. and Seinfeld,~J H.: Parameterization of cloud droplet formation in global climate models, J. Geophys. Res., 108, 4415, \doi4410.1029/2002JD002911, 2003. Pruppacher,~H R. and Klett,~J D.: Microphysics of clouds and precipitation 2nd edn., Kluwer Academic Publishers, Boston, MA, 954 pp., 1997. Seinfeld,~J H. and Pandis,~S N.: Atmospheric Chemistry and Physics, John Wiley and Sons, New York, NY, USA, 1998. Twomey,~S.: The nuclei of natural cloud formation. II. The supersaturation in natural clouds and the variation of cloud droplet number concentration, Pure Appl. Geophys., 43, 243–249, \doi210.1007/BF01993560, 1959.