Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 4 2008 10.5194/acpd-8-12721-2008 http://www.atmos-chem-phys-discuss.net/8/12721/2008/ http://www.atmos-chem-phys-discuss.net/8/12721/2008/acpd-8-12721-2008.html http://www.atmos-chem-phys-discuss.net/8/12721/2008/acpd-8-12721-2008.pdf 12721 12736 2008-07-04 Cloud processing, cloud evaporation and Angström exponent G.-J. Roelofs g.j.h.roelofs@uu.nl V. Kamphuis Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands With a cloud parcel model we investigated how cloud processing and cloud evaporation modify the size distribution and the Angström exponent of an aerosol population. Cloud processing causes a decrease in particle concentrations, relatively most efficiently in the coarse mode, and reduces the relative dispersion of the aerosol distribution. As a result the Angström exponent of the aerosol increases. The Angström exponent is subject to other influences. It is very sensitive for relative humidity, especially between 95% and 100%. In addition, kinetic limitations delay droplet evaporation during cloud dissipation, which hampers a direct relation between the Angström exponent and the relative humidity. Consequently, a direct interpretation of the Angström exponent in terms of aerosol properties that play a role in aerosol-cloud interactions, such as the fine mode fraction, is rather complex. Albrecht, B. A.: Aerosols, cloud microphysics and fractional cloudiness, Science, 245, 1227–1230, 1989. Anderson, T. L., Wu, Y., Chu, D. A., Schmid, B., Redemann, J., and Dubovik, O.: Testing the MODIS satellite retrieval of aerosol fine-mode fraction, J. Geophys. Res., 110, D18204, doi:10.1029/2005JD005978, 2005. Bréon, F. M., Tanré, D., and Generoso, S.: Aerosol effects on cloud droplet size monitored from satellite, Science, 295, 834–838, 2002. Charlson, R. J., Schwarz, S. E., Hales, J. M., Cess, R. D., Coakley Jr., J. A., Hansen, J. E., and Hofmann, D. J.: Climate forcing by anthropogenic aerosols, Science, 255, 423–430, 1992. Charlson, R. J., Ackerman, A. S., Bender, F. A. M., Anderson, T. L., and Liu, Z.: On the climate forcing consequences of the albedo continuum between cloudy and clear air, Tellus, 59, 715–727, 2007. Chuang, P. Y., Charlson, R. J., and Seinfeld, J. H.: Kinetic limitations on droplet formation in clouds, Nature, 390, 594–596, 1997. Feingold, G. and Kreidenweis, S. M.: Cloud processing of aerosol as modeled by a large eddy simulation with coupled microphysics and aqueous chemistry, J. Geophys. Res., 107(D23), 4687, doi:10.1029/2002JD002054, 2002. Fukuta, N. and Walter, N. A.: Kinetics of hydrometeor growth from a vapor spherical model, J. Atmos. Sci., 27, 1160–1172, 1970. Hänel, G.: The role of aerosol properties during the condensational stage of cloud: a reinvestigation of numerics and microphysics, Beitr. Phys. Atmosph., 60, 321–339, 1987. Jacobson, M. Z.: Fundamentals of atmospheric modeling, Cambridge University Press, New York, USA, 426–452, 1998. Kaufman, Y. J., Tanré, D., and Boucher, O.: A satellite view of aerosols in the climate system, Nature, 419, 215–223, 2002. Kaufman, Y. J., Boucher, O., Tanré, D., Chin, M., Remer, L. A., and Takemura, L.: Aerosol anthropogenic component estimated from satellite data, Geophys. Res. Lett., 32, L17804, doi:10.1029/2005GL023125, 2005. Koren, I., Remer, L. A., Kaufman, Y. J., Rudich, Y., and Vanderlei Martins, J.: On the twilight zone between clouds and aerosols, Geophys. Res. Lett., 34, L08805, doi:10.1029/2007GL029253, 2007. Kulmala, M., Laaksonen, A., Korhonen, P., Ahonen, T., and Baret, J.: The effect of atmospheric nitric acid vapor on cloud condensation nucleus activation, J. Geophys. Res., 98, 22 949–22 958, 1993. Loeb, N. G. and G. L. Schuster: An observational study of the relationship between cloud, aerosol and meteorology in broken low-level cloud conditions, J. Geophys. Res., doi:10.1029/2007JD009763, in press, 2008. Lohmann, U., Quaas, J., Kinne, S., and Feichter, J.: Different approaches for constraining global climate models of the anthropogenic indirect aerosol effect, Bull. Amer. Meteor. Soc., 88, 243–249, 2007. Lu, M. L., Wang, J., Freedman, A., Jonsson, H. H., Flagan, R. C., McClatchey, R. A., and Seinfeld, J. H.: Analysis of humidity halos around trade wind cumulus clouds, J. Atm. Sci., 60, 1041–1059, 2003. Myhre, G., Stordal, F., Johnsrud, M., Kaufman, Y. J., Rosenfeld, D., Storelvmo, T., Kristjánsson, J., Berntsen, T., Myhre, A., and Isaksen, I. S. A.: Aerosol-cloud interaction inferred from MODIS satellite data and global aerosol models, Atmos. Chem. Phys., 7, 3081–3101, 2007. Nakajima, T., Higurashi, A., Kawamoto, K., and Penner, J. E.: A possible correlation between satellite-derived cloud and aerosol microphysical parameters, Geophys. Res. Lett., 28, 1171–1174, 2001. Quaas, J., Boucher, O., Bellouin, N., and Kinne, S.: Satellite-based estimate of the direct and indirect aerosol climate forcing, J. Geophys. Res., 113, D05204, doi:10.1029/2007JD008962, 2008. Roelofs, G. J., On the drop and aerosol size dependence of aqueous sulfate formation in a continental cumulus cloud, Atmos. Environ., 26A, 2309–2321, 1992. Roelofs, G. J. and Jongen, S.: A model study of the influence of aerosol size and chemical properties on precipitation formation in warm clouds, J. Geophys. Res., 109, D22201, doi:10.1029/2004JD004779, 2004. Schuster, G. L., Dubovik, O., and Holben, B. N.: Angström exponent and bimodal aerosol size distributions, J. Geophys. Res., 111, D07207, doi:10.1029/2005JD006328, 2006. Solomon, S., Qin, D., Manning, M., et al.: Technical summary, in: Climate Change 2007: the physical science basis: contribution of working group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK and New York, NY, USA, 2007. Stier, P., Feichter, J., Kinne, S., Kloster, S., Vignati, E., Wilson, J., Ganzeveld, L., Tegen, I., Werner, M., Balkanski, Y., Schulz, M., and Boucher, O.: The aerosol-climate model ECHAM5-HAM, Atmos. Chem. Phys., 5, 1125–1156, 2005. Twomey, S.: Pollution and the planetary albedo, Atmos. Environ., 8, 1251–1256, 1974. Van de Hulst, H. C.: Light scattering by small particles, Wiley, New York, USA, 176–178, 1957.