ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-8791-2009 Influence of entrainment of CCN on microphysical properties of warm cumulus Derksen J. W. B. 1 Roelofs G.-J. H. 1 Röckmann T. 1 Institute for Marine and Atmospheric Research Utrecht, Utrecht, The Netherlands 02 04 2009 9 2 8791 8816 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/9/8791/2009/acpd-9-8791-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/8791/2009/acpd-9-8791-2009.pdf

We use a 1-D cloud model with explicit microphysics and a binned representation of the aerosol size distribution to investigate the influence of entrainment of cloud condensation nuclei (CCN) on the microphysical development of warm cumulus clouds. For a more realistic representation of cloud drop spectral width, the model separates droplets that grow on aerosol that is initially present in the cloud from droplets growing on entrained aerosol. Model results are compared with observations of trade wind cumulus microphysics from the Rain in Cumulus over the Ocean experiment (RICO, 2004–2005). The results indicate that CCN are entrained throughout the entire cloud depth, and inside the cloud part of these may be activated. Compared to a simulation where entrainment of ambient CCN is neglected this leads to higher cloud droplet number concentrations (CDNC) and a continuous presence of droplets in the range smaller than ~5 μm that is consistent with the observations. Cloud dynamics are sensitive to the entrainment parameter as well as to the applied initial vertical velocity, as expressed by the liquid water content and cloud top height. However, simulated cloud drop spectra remain relatively unaffected for the specific conditions during RICO.

 References Albrecht, B A.: Aerosols, cloud microphysics, and fractional cloudiness, Science, 245, 1227–1230, 1989. Arabas, S., Pawlowska, H., and Grabowski, W W.: Effective radius and droplet spectral width from in-situ aircraft observations in trade-wind cumuli during RICO, Geophys. Res. Lett., submitted, 2009. Blyth, A M. and Latham, J.: Airborne studies of the altitudinal variability of the microphysical structure of small, ice-free, Montanan cumulus clouds, Q. J. Roy. Meteor. Soc., 116, 1405–1423, doi:10.1002/qj.49711649608, 1990. Burnet, F. and Brenguier, J.-L.: Observational study of the entrainment-mixing process in warm convective clouds, J. Atmos. Sci., 64, 1995–2011, 2007. Charlson, R J., Schwarz, S E., Hales, J M., Cess, R D., Jr., J. A C., Hansen, J E., and Hofmann, D J.: Climate forcing by anthropogenic aerosols, Science, 255, 423–430, 1992. Fountoukis, C. and Nenes, A.: Continued development of a cloud droplet formation parameterization for global climate models, J. Geophys. Res., 110, D11212, doi:10.1029/2004JD005591, 2005. Gerber, H., Frick, G., Malinowski, S P., Brenguier, J.-L., and Burnet, F.: Holes and entrainment in stratocumulus, J. Atmos. Sci., 62, 443–459, 2005. Gerber, H., Frick, G., Jensen, J B., and Hudson, J G.: Entrainment, mixing and microphysics in trade-wind cumulus, J. Meteorol. Soc. Jpn., 86A, 87–106, 2008. Grits, B., Pinsky, M., and Khain, A.: Investigation of small-scale droplet concentration inhomogeneities in a turbulent flow, Meteor. Atmos. Phys., 92, 191–204, doi:10.1007/s00703-005-0157-4, 2006. 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. Hicks, E., Pontikis, C., and Rigaud, A.: Entrainment and mixing processes as related to droplet growth in warm midlatitude and tropical clouds, J. Atmos. Sci., 47, 1589–1618, 1990. Hudson, J G. and Mishra, S.: Relationship between CCN and cloud microphysics variations in clean maritime air, Geophys. Res. Lett., 34, L16804, doi:10.1029/2007GL030044, 2007. Hudson, J G. and Yum, S S.: Droplet spectral broadening in Marine Stratus, J. Atmos. Sci., 54, 2642–2654, 1997. Jacobson, M Z.: Fundamentals of Atmospheric Modeling, Cambridge Univ. Press, New York, 1998. Kreidenweis, S., Walcek, C., Feingold, G., Gong, W., Jacobson, M., Kim, C., Liu, X., Penner, J., Nenes, A., and Seinfeld, J.: Modification of aerosol mass and size distribution due to aqueous phase SO<sub>2</sub> oxidation in clouds: Comparisons of several models, J. Geophys. Res., 108, 4213, doi:10.1029/2002JD002697, 2003. Krueger, S K., Su, C.-W., and McMurtry, P A.: Modeling entrainment and finescale mixing in cumulus clouds, J. Atmos. Sci., 54, 2697–2712, 1997. 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, 22949–22958, 1993. Lohmann, U. and Feichter, J.: Global indirect aerosol effects: a review, Atmos. Chem. Phys., 5, 715–737, 2005. 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. Atmos. Sci., 60, 1041–1059, 2003. Meskhidze, N., Nenes, A., Conant, W C., and Seinfeld, J H.: Evolution of a new cloud droplet activation parameterization with in situ data from CRYSTAL-FACE and CSTRIPE, J. Geophys. Res., 110, D16202, doi:10.1029/2004JD005703, 2005. Ogura, Y. and Takahashi, T.: Numerical simulation of the life cycle of a thunderstorm cell, Mon. Weather Rev., 99, 895–911, 1971. Paluch, I R.: Mixing and the cloud droplet size spectrum: Generalizations from the CCOPE data, J. Atmos. Sci., 43, 1984–1993, 1986. Penner, J E. and Chuang, C C.: The role of entrainment and mixing in altering the relationship between aerosol concentration and cloud drop number concentration, Ninth ARM Science Team Meeting Proceedings, 1999. Peter, J R., Blyth, A M., Brooks, B., McQuaid, J B., Lingard, J. J N., and Smith, M H.: On the composition of Caribbean maritime aerosol particles measured during RICO, Q. J. Roy. Meteor. Soc., 134, 1059–1063, doi:10.1002/qj.198, 2008. Pinsky, M. and Khain, A.: Fine structure of cloud droplet concentrations as seen from the fast-FSSP measurements. Part II: Results of in situ observations, J. Appl. Meteorol., 42(1), 65–73, 2003. Pruppacher, H R. and Klett, J D.: Microphysics of clouds and precipitation, D. Reidel, Dordrecht, 1978. Rauber, R., Stevens, B., Ochs, H., Knight, C., Albrecht, B., Blyth, A., Fairall, C., Jensen, J., Lasher-Trapp, S., Mayol-Bracero, O., Vali, G., Anderson, J., Baker, B., Bandy, A., Burnet, E., Brenguier, J., Brewer, W., Brown, P., Chuang, P., Cotton, W., Girolamo, L D., Geerts, B., Gerber, H., Gške, S., Gomes, L., Heikes, B., Hudson, J., Kollias, P., Lawson, R., Krueger, S., Lenschow, D., Nuijens, L., O'Sullivan, D., Rilling, R., Rogers, D., Siebesma, A., Snodgrass, E., Stith, J., Thornton, D., Tucker, S., Twohy, C., and Zuidema, P.: Rain In Shallow Cumulus over the Ocean: The RICO Campaign, B. Am. Meteorol. Soc., 88, 1912–1928, 2007. 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. Roelofs, G.-J. and Kamphuis, V.: Cloud processing, cloud evaporation and Angström exponent, Atmos. Chem. Phys., 9, 71–80, 2009. Roesner, S., Flossmann, A I., and Pruppacher, H R.: The effect on the evolution of the drop spectrum in clouds of the preconditioning of air by successive convective elements, Q. J. Roy. Meteor. Soc., 116, 1389–1403, doi:10.1002/qj.49711649607, 1990. Segal, Y., Pinsky, M., Khain, A., and Erlick, C.: Thermodynamic factors influencing bimodal spectrum formation in cumulus clouds, Atmos. Res., 66, 43–64, 2003. Solomon, S., Qin, D., Manning, M., Alley, R B., Berntsen, T., Bindoff, N L., Chen, Z., Chidthaisong, A., Gregory, J M., Hegerl, G C., Heimann, H., Hewitson, B., Hoskins, B J., Joos, F., Jouzel, J., Kattsov, V., Lohmann, U., Matsuno, T., Molina, M., Nichollsand, N., Overpeck, J., Raga, G., Ramaswamy, V., Ren, J., Rusticucci, M., Somerville, R., Stocker, T F., Whetton, P. A. W R., and Wratt, D.: 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 Univ. Press, Cambridge, United Kingdom and New York, NY, USA, 2007. Su, C.-W., Krueger, S K., McMurtry, P A., and Austin, P H.: Linear eddy modeling of droplet spectral evolution during entrainment and mixing in cumulus clouds, Atmos. Res., 47-48, 41–58, 1998. Takahashi, T.: Warm rain, giant nuclei and chemical balance -a numerical model, J. Atmos. Sci., 33, 269–286, 1976. Twomey, S.: The influence of pollution on the shortwave albedo of clouds, J. Atmos. Sci., 34, 1149–1154, 1977.