ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-8777-2012 Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem Yang Q. 1 Gustafson Jr. W. I. 1 Fast J. D. 1 Wang H. 1 Easter R. C. 1 Wang M. 1 Ghan S. J. 1 Berg L. K. 1 Leung L. R. 1 Morrison H. 2 Pacific Northwest National Laboratory, Richland, WA, USA National Center for Atmospheric Research, Boulder, CO, USA 28 09 2012 12 18 8777 8796 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.net/12/8777/2012/acp-12-8777-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/8777/2012/acp-12-8777-2012.pdf

Cloud-system resolving simulations with the chemistry version of the Weather Research and Forecasting (WRF-Chem) model are used to quantify the relative impacts of regional anthropogenic and oceanic emissions on changes in aerosol properties, cloud macro- and microphysics, and cloud radiative forcing over the Southeast Pacific (SEP) during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) (15 October–16 November 2008). Two distinct regions are identified. The near-coast polluted region is characterized by low surface precipitation rates, the strong suppression of non-sea-salt particle activation due to sea-salt particles, a predominant albedo effect in aerosol indirect effects, and limited impact of aerosols associated with anthropogenic emissions on clouds. Opposite sensitivities to natural marine and anthropogenic aerosol perturbations are seen in cloud properties (e.g., cloud optical depth and cloud-top and cloud-base heights), precipitation, and the top-of-atmosphere and surface shortwave fluxes over this region. The relatively clean remote region is characterized by large contributions of aerosols from non-regional sources (lateral boundaries) and much stronger drizzle at the surface. Under a scenario of five-fold increase in regional anthropogenic emissions, this relatively clean region shows large cloud responses, for example, a 13% increase in cloud-top height and a 9% increase in albedo in response to a moderate increase (25% of the reference case) in cloud condensation nuclei (CCN) concentration. The reduction of precipitation due to this increase in anthropogenic aerosols more than doubles the aerosol lifetime in the clean marine boundary layer. Therefore, the aerosol impacts on precipitation are amplified by the positive feedback of precipitation on aerosol, which ultimately alters the cloud micro- and macro-physical properties, leading to strong aerosol-cloud-precipitation interactions. The high sensitivity is also related to an increase in cloud-top entrainment rate (by 16% at night) due to the increased anthropogenic aerosols. The simulated aerosol-cloud-precipitation interactions due to the increased anthropogenic aerosols have a stronger diurnal cycle over the clean region compared to the near-coast region with stronger interactions at night. During the day, solar heating results in more frequent decoupling of the cloud and sub-cloud layers, thinner clouds, reduced precipitation, and reduced sensitivity to the increase in anthropogenic emissions. This study shows the importance of natural aerosols in accurately quantifying anthropogenic forcing within a regional modeling framework. The results of this study also imply that the energy balance perturbations from increased anthropogenic emissions are larger in the more susceptible clean environment than in already polluted environment and are larger than possible from the first indirect effect alone.

 References Abdul-Razzak, H. and Ghan, S. J.: A parameterization of aerosol activation 2. Multiple aerosol types, J. Geophys. Res., 105, 6837–6844, http://dx.doi.org/10.1029/1999JD901161doi:10.1029/1999JD901161, 2000. Ackerman, A. S., Toon, O. B., Stevens, D. E., and Coakley, J. A.: Enhancement of cloud cover and suppression of nocturnal drizzle in stratocumulus polluted by haze, Geophys. Res. Lett., 30, 1381, http://dx.doi.org/10.1029/2002gl016634doi:10.1029/2002gl016634, 2003. Ackerman, A. S., Kirkpatrick, M. P., Stevens, D. E., and Toon, O. B.: The impact of humidity above stratiform clouds on indirect aerosol climate forcing, Nature, 432, 1014–1017, http://dx.doi.org/10.1038/Nature03174doi:10.1038/Nature03174, 2004. Albrecht, B. A.: Aerosols, Cloud Microphysics, and Fractional Cloudiness, Science, 245, 1227–1230, 1989. Allen, G., Coe, H., Clarke, A., Bretherton, C., Wood, R., Abel, S. J., Barrett, P., Brown, P., George, R., Freitag, S., McNaughton, C., Howell, S., Shank, L., Kapustin, V., Brekhovskikh, V., Kleinman, L., Lee, Y.-N., Springston, S., Toniazzo, T., Krejci, R., Fochesatto, J., Shaw, G., Krecl, P., Brooks, B., McMeeking, G., Bower, K. N., Williams, P. I., Crosier, J., Crawford, I., Connolly, P., Allan, J. D., Covert, D., Bandy, A. R., Russell, L. M., Trembath, J., Bart, M., McQuaid, J. B., Wang, J., and Chand, D.: South East Pacific atmospheric composition and variability sampled along 20° S during VOCALS-REx, Atmos. Chem. Phys., 11, 5237–5262, http://dx.doi.org/10.5194/acp-11-5237-2011doi:10.5194/acp-11-5237-2011, 2011. Baker, M. B. and Charlson, R. J.: Bistability of CCN Concentrations and Thermodynamics in the Cloud-topped Boundary-Layer, Nature, 345, 142–145, 1990. Barnard, J. C., Fast, J. D., Paredes-Miranda, G., Arnott, W. P., and Laskin, A.: Technical Note: Evaluation of the WRF-Chem "Aerosol Chemical to Aerosol Optical Properties" Module using data from the MILAGRO campaign, Atmos. Chem. Phys., 10, 7325–7340, http://dx.doi.org/10.5194/acp-10-7325-2010doi:10.5194/acp-10-7325-2010, 2010. Berner, A. H., Bretherton, C. S., and Wood, R.: Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06, Atmos. Chem. Phys., 11, 10525–10540, http://dx.doi.org/10.5194/acp-11-10525-2011doi:10.5194/acp-11-10525-2011, 2011. Blomquist, B. W., Fairall, C. W., Huebert, B. J., Kieber, D. J., and Westby, G. R.: DMS sea-air transfer velocity: Direct measurements by eddy covariance and parameterization based on the NOAA/COARE gas transfer model, Geophys. Res. Lett., 33, L07601, http://dx.doi.org/10.1029/2006gl025735doi:10.1029/2006gl025735, 2006. Boutle, I. A. and Abel, S. J.: Microphysical controls on the stratocumulus topped boundary-layer structure during VOCALS-REx, Atmos. Chem. Phys., 12, 2849–2863, http://dx.doi.org/10.5194/acp-12-2849-2012doi:10.5194/acp-12-2849-2012, 2012. Bretherton, C. S. and Wyant, M. C.: Moisture transport, lower-tropospheric stability, and decoupling of cloud-topped boundary layers, J. Atmos. Sci., 54, 148–167, 1997. Bretherton, C. S., Blossey, P. N., and Uchida, J.: Cloud droplet sedimentation, entrainment efficiency, and subtropical stratocumulus albedo, Geophys. Res. Lett., 34, L03813, http://dx.doi.org/10.1029/2006gl027648doi:10.1029/2006gl027648, 2007. Bretherton, C. S., Uchida, J., and Blossey, P. N.: Slow manifolds and multiple equilibria in stratocumulus-capped boundary layers, J. Adv. Model. Earth Syst., 2, 14, 20 pp., http://dx.doi.org/10.3894/JAMES.2010.2.14doi:10.3894/JAMES.2010.2.14, 2010a. Bretherton, C. S., Wood, R., George, R. C., Leon, D., Allen, G., and Zheng, X.: Southeast Pacific stratocumulus clouds, precipitation and boundary layer structure sampled along 20° S during VOCALS-REx, Atmos. Chem. Phys., 10, 10639–10654, http://dx.doi.org/10.5194/acp-10-10639-2010doi:10.5194/acp-10-10639-2010, 2010b. Chand, D., Hegg, D. A., Wood, R., Shaw, G. E., Wallace, D., and Covert, D. S.: Source attribution of climatically important aerosol properties measured at Paposo (Chile) during VOCALS, Atmos. Chem. Phys., 10, 10789–10801, http://dx.doi.org/10.5194/acp-10-10789-2010doi:10.5194/acp-10-10789-2010, 2010. Clarke, A. D., Owens, S. R., and Zhou, J. C.: An ultrafine sea- salt flux from breaking waves: Implications for cloud condensa- tion nuclei in the remote marine atmosphere, J. Geophys. Res.-Atmos., 111, D06202, http://dx.doi.org/10.1029/2005jd006565doi:10.1029/2005jd006565, 2006. Chapman, E. G., Gustafson Jr., W. I., Easter, R. C., Barnard, J. C., Ghan, S. J., Pekour, M. S., and Fast, J. D.: Coupling aerosol-cloud-radiative processes in the WRF-Chem model: Investigating the radiative impact of elevated point sources, Atmos. Chem. Phys., 9, 945–964, http://dx.doi.org/10.5194/acp-9-945-2009doi:10.5194/acp-9-945-2009, 2009. Charlson, R. J., Lovelock, J. E., Andreae, M. O., and Warren, S. G.: Oceanic Phytoplankton, Atmospheric Sulfur, Cloud Albedo and Climate, Nature, 326, 655–661, 1987. Chen, Y.-C., Xue, L., Lebo, Z. J., Wang, H., Rasmussen, R. M., and Seinfeld, J. H.: A comprehensive numerical study of aerosol-cloud-precipitation interactions in marine stratocumulus, Atmos. Chem. Phys., 11, 9749–9769, http://dx.doi.org/10.5194/acp-11-9749-2011doi:10.5194/acp-11-9749-2011, 2011. de Szoeke, S. P., Fairall, C. W., Wolfe, D. E., Bariteau, L., and Zuidema, P.: Surface Flux Observations on the Southeastern Tropical Pacific Ocean and Attribution of SST Errors in Coupled Ocean-Atmosphere Models, J. Climate, 23, 4152–4174, http://dx.doi.org/10.1175/2010jcli3411.1doi:10.1175/2010jcli3411.1, 2010. Fast, J. D., Gustafson, W. I., Easter, R. C., Zaveri, R. A., Barnard, J. C., Chapman, E. G., Grell, G. A., and Peckham, S. E.: Evolution of ozone, particulates, and aerosol direct radiative forcing in the vicinity of Houston using a fully coupled meteorology-chemistry-aerosol model, J. Geophys. Res.-Atmos., 111, D21305, http://dx.doi.org/10.1029/2005jd006721doi:10.1029/2005jd006721, 2006. Fast, J. D., Gustafson Jr., W. I., Berg, L. K., Shaw, W. J., Pekour, M., Shrivastava, M., Barnard, J. C., Ferrare, R. A., Hostetler, C. A., Hair, J. A., Erickson, M., Jobson, B. T., Flowers, B., Dubey, M. K., Springston, S., Pierce, R. B., Dolislager, L., Pederson, J., and Zaveri, R. A.: Transport and mixing patterns over Central California during the carbonaceous aerosol and radiative effects study (CARES), Atmos. Chem. Phys., 12, 1759–1783, http://dx.doi.org/10.5194/acp-12-1759-2012doi:10.5194/acp-12-1759-2012, 2012. Feingold, G., Cotton, W. R., Kreidenweis, S. M., and Davis, J. T.: The impact of giant cloud condensation nuclei on drizzle formation in stratocumulus: Implications for cloud radiative properties, J. Atmos. Sci., 56, 4100–4117, 1999. Feingold, G., Remer, L. A., Ramaprasad, J., and Kaufman, Y. J.: Analysis of smoke impact on clouds in Brazilian biomass burning regions: An extension of Twomey's approach, J. Geophys. Res., 106, 22907–22922, 2001. Feingold, G., Eberhard, W. L., Veron, D. E., and Previdi, M.: First measurements of the Twomey indirect effect using ground-based remote senors, Geophys. Res. Lett., 30, 1287, http://dx.doi.org/10.1029/2002GL016633doi:10.1029/2002GL016633, 2003. Freud, E. and Rosenfeld, D.: Linear relation between convective cloud drop number concentration and depth for rain initiation, J. Geophys. Res.-Atmos., 117, D02207, http://dx.doi.org/10.1029/2011jd016457doi:10.1029/2011jd016457, 2012. Gao, Y., Liu, X., Zhao, C., and Zhang, M.: Emission controls versus meteorological conditions in determining aerosol concentrations in Beijing during the 2008 Olympic Games, Atmos. Chem. Phys., 11, 12437–12451, http://dx.doi.org/10.5194/acp-11-12437-2011doi:10.5194/acp-11-12437-2011, 2011. Ghan, S. J., Guzman, G., and Abdul-Razzak, H.: Competition between sea salt and sulfate particles as cloud condensation nuclei, J. Atmos. Sci., 55, 3340–3347, 1998. Gong, S. L., Barrie, L. A., and Blanchet, J. P.: Modeling sea-salt aerosols in the atmosphere .1. Model development, J. Geophys. Res.-Atmos., 102, 3805–3818, 1997. Grell, G. A., Peckham, S. E., Schmitz, R., McKeen, S. A., Frost, G., Skamarock, W. C., and Eder, B.: Fully coupled "online" chemistry within the WRF model, Atmos. Environ., 39, 6957–6975, http://dx.doi.org/10.1016/j.atmosenv.2005.04.027doi:10.1016/j.atmosenv.2005.04.027, 2005. Gustafson, W. I., Chapman, E. G., Ghan, S. J., Easter, R. C., and Fast, J. D.: Impact on modeled cloud characteristics due to simplified treatment of uniform cloud condensation nuclei during NEAQS 2004, Geophys. Res. Lett., 34, L19809, http://dx.doi.org/10.1029/2007gl030021doi:10.1029/2007gl030021, 2007. Hawkins, L. N., Russell, L. M., Covert, D. S., Quinn, P. K., and Bates, T. S.: Carboxylic acids, sulfates, and organosulfates in processed continental organic aerosol over the southeast Pacific Ocean during VOCALS-REx 2008, J. Geophys. Res.-Atmos., 115, D13201, http://dx.doi.org/10.1029/2009jd013276doi:10.1029/2009jd013276, 2010. Hill, A. A., Feingold, G., and Jiang, H. L.: The Influence of Entrainment and Mixing Assumption on Aerosol-Cloud Interactions in Marine Stratocumulus, J. Atmos. Sci., 66, 1450–1464, http://dx.doi.org/10.1175/2008jas2909.1doi:10.1175/2008jas2909.1, 2009. Hong, S. Y., Noh, Y., and Dudhia, J.: A new vertical diffusion package with an explicit treatment of entrainment processes, Mon. Weather Rev., 134, 2318–2341, 2006. Jones, C. R., Bretherton, C. S., and Leon, D.: Coupled vs. decoupled boundary layers in VOCALS-REx, Atmos. Chem. Phys., 11, 7143–7153, http://dx.doi.org/10.5194/acp-11-7143-2011doi:10.5194/acp-11-7143-2011, 2011. Kazil, J., Wang, H., Feingold, G., Clarke, A. D., Snider, J. R., and Bandy, A. R.: Modeling chemical and aerosol processes in the transition from closed to open cells during VOCALS-REx, Atmos. Chem. Phys., 11, 7491–7514, http://dx.doi.org/10.5194/acp-11-7491-2011doi:10.5194/acp-11-7491-2011, 2011. Khairoutdinov, M., and Y. Kogan: A new cloud physics parameterization in a large-eddy simulation model of marine stratocumulus, Mon. Weather Rev., 128, 229–243, 2000. Klein, S. A. and Hartmann, D. L.: The seasonal cycle of low stratiform clouds, J. Climate, 6, 1587–1606, 1993. Kleinman, L. I., Daum, P. H., Lee, Y.-N., Lewis, E. R., Sedlacek III, A. J., Senum, G. I., Springston, S. R., Wang, J., Hubbe, J., Jayne, J., Min, Q., Yum, S. S., and Allen, G.: Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx, Atmos. Chem. Phys., 12, 207–223, http://dx.doi.org/10.5194/acp-12-207-2012doi:10.5194/acp-12-207-2012, 2012. Kogan, Y. L., Mechem, D. B., and Choi, K.: Effects of sea-salt aerosols on precipitation in siumulations of shallow cumulus, J. Atmos. Sci, 69, 463–483, http://dx.doi.org/10.1175/JAS-D-11-031.1doi:10.1175/JAS-D-11-031.1, 2012. L'Ecuyer, T. S., Berg, W., Haynes, J., Lebsock, M., and Takemura, T.: Global observations of aerosol impacts on precipitation occurrence in warm maritime clouds, J. Geophys. Res.-Atmos., 114, D09211, http://dx.doi.org/10.1029/2008jd011273doi:10.1029/2008jd011273, 2009. Loeb, N. G. and Schuster, G. L.: An observational study of the relationship between cloud, aerosol and meteorology in broken low-level cloud conditions, J. Geophys. Res., 113, D14214, http://dx.doi.org/10.1029/2007JD009763doi:10.1029/2007JD009763, 2008. Lu, M. L. and Seinfeld, J. H.: Study of the aerosol indirect effect by large-eddy simulation of marine stratocumulus, J. Atmos. Sci., 62, 3909–3932, 2005. Manton, M. J. and Cotton, W. R.: Parameterization of the atmospheric surface layer, J. Atmos. Sci., 34, 331–334, 1977. Matsui, T., Masunaga, H., Kreidenweis, S. M., Pielke, R. A., Tao, W. K., Chin, M., and Kaufman, Y. J.: Satellite-based assessment of marine low cloud variability associated with aerosol, atmospheric stability, and the diurnal cycle, J Geophys Res-Atmos, 111, D20202, http://dx.doi.org/10.1029/2006jd008056doi:10.1029/2006jd008056, 2006. Mechem, D. B., Yuter, S. E., and de Szoeke, S. P.: Thermodynamic and aerosol controls in Southeast Pacific Stratocumulus, J. Atmos. Sci., 69, 1250-1266, http://dx.doi.org/10.1175/JAS-D-11-0165.1doi:10.1175/JAS-D-11-0165.1, 2012. Monahan, E. C., Spiel, D. E., and Davidson, K. L.: A model of marine aerosol generation via whitecaps and wave disruption, in: Oceanic Whitecaps, edited by: Niocail, E. C. M. a. G. M., Reidel, D., Norwell, 167–174, 1986. Morrison, H., Thompson, G., and Tatarskii, V.: Impact of Cloud Microphysics on the Development of Trailing Stratiform Precipitation in a Simulated Squall Line: Comparison of One- and Two-Moment Schemes, Mon. Weather Rev., 137, 991–1007, http://dx.doi.org/10.1175/2008mwr2556.1doi:10.1175/2008mwr2556.1, 2009. Nicholls, S.: The Dynamics of Stratocumulus – Aircraft Observations and Comparisons with a Mixed Layer Model, Q. J. Roy. Meteor. Soc., 110, 783–820, 1984. Nightingale, P. D., Malin, G., Law, C. S., Watson, A. J., Liss, P. S., Liddicoat, M. I., Boutin, J., and Upstill-Goddard, R. C.: In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers, Global Biogeochem. Cy., 14, 373–387, 2000. Noh Y., Gheon, W. G., Hong, S. Y., and Raasch, S.: Improvement of the K-profile model for the planetary boundary layer based on large eddy simulation data, Bound.-Lay. Meteorol., 107, 401–427, 2003. Painemal, D. and Zuidema, P.: Microphysical variability in southeast Pacific Stratocumulus clouds: synoptic conditions and radiative response, Atmos. Chem. Phys., 10, 6255–6269, http://dx.doi.org/10.5194/acp-10-6255-2010doi:10.5194/acp-10-6255-2010, 2010. Penner, J. E., Xu, L., and Wang, M. H.: Satellite methods underestimate indirect climate forcing by aerosols, P. Natl. Acad. Sci. USA, 108, 13404–13408, 2011. Pincus, R. and Baker, M. B.: Effect of Precipitation on the Albedo Susceptibility of Clouds in the Marine Boundary-Layer, Nature, 372, 250–252, 1994. Pinsky, M. B. and Khain, A. P.: Effects of in-cloud nucleation and turbulence on droplet spectrum formation in cumulus clouds, Q. J. Roy. Meteor. Soc., 128, 501–533, 2002. Qian, Y., Gustafson, W. I., Leung, L. R., and Ghan, S. J.: Effects of soot-induced snow albedo change on snowpack and hydrological cycle in western United States based on Weather Research and Forecasting chemistry and regional climate simulations, J. Geophys. Res.-Atmos., 114, D03108, http://dx.doi.org/10.1029/2008jd011039doi:10.1029/2008jd011039, 2009. Quaas, J., Ming, Y., Menon, S., Takemura, T., Wang, M., Penner, J. E., Gettelman, A., Lohmann, U., Bellouin, N., Boucher, O., Sayer, A. M., Thomas, G. E., McComiskey, A., Feingold, G., Hoose, C., Kristjánsson, J. E., Liu, X., Balkanski, Y., Donner, L. J., Ginoux, P. A., Stier, P., Grandey, B., Feichter, J., Sednev, I., Bauer, S. E., Koch, D., Grainger, R. G., Kirkevåg, A., Iversen, T., Seland, Ø., Easter, R., Ghan, S. J., Rasch, P. J., Morrison, H., Lamarque, J.-F., Iacono, M. J., Kinne, S., and Schulz, M.: Aerosol indirect effects – general circulation model intercomparison and evaluation with satellite data, Atmos. Chem. Phys., 9, 8697–8717, http://dx.doi.org/10.5194/acp-9-8697-2009doi:10.5194/acp-9-8697-2009, 2009. Raes, F.: Entrainment of free tropospheric aerosols as a regulating mechanism for cloud condensation nuclei in the remote marine boundary layer, J. Geophys. Res., 100, 2893–2903, http://dx.doi.org/10.1029/94JD02832doi:10.1029/94JD02832, 1995. Rahn, D. A. and Garreaud, R.: Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 1: Mean structure and diurnal cycle, Atmos. Chem. Phys., 10, 4491–4506, http://dx.doi.org/10.5194/acp-10-4491-2010doi:10.5194/acp-10-4491-2010, 2010. Rosenfeld, D., Lahav, R., Khain, A., and Pinsky, M.: The role of sea spray in cleansing air pollution over ocean via cloud processes, Science, 297, 1667–1670, http://dx.doi.org/10.1126/Science.1073869doi:10.1126/Science.1073869, 2002. Saide, P. E., Spak, S. N., Carmichael, G. R., Mena-Carrasco, M. A., Yang, Q., Howell, S., Leon, D. C., Snider, J. R., Bandy, A. R., Collett, J. L., Benedict, K. B., de Szoeke, S. P., Hawkins, L. N., Allen, G., Crawford, I., Crosier, J., and Springston, S. R.: Evaluating WRF-Chem aerosol indirect effects in Southeast Pacific marine stratocumulus during VOCALS-REx, Atmos. Chem. Phys., 12, 3045–3064, http://dx.doi.org/10.5194/acp-12-3045-2012doi:10.5194/acp-12-3045-2012, 2012. Sandu, I., Brenguier, J. L., Geoffroy, O., Thouron, O., and Masson, V.: Aerosol impacts on the diurnal cycle of marine stratocumulus, J. Atmos. Sci., 65, 2705–2718, http://dx.doi.org/10.1175/2008jas2451.1doi:10.1175/2008jas2451.1, 2008. Shank, L. M., Howell, S., Clarke, A. D., Freitag, S., Brekhovskikh, V., Kapustin, V., McNaughton, C., Campos, T., and Wood, R.: Organic matter and non-refractory aerosol over the remote Southeast Pacific: oceanic and combustion sources, Atmos. Chem. Phys., 12, 557–576, http://dx.doi.org/10.5194/acp-12-557-2012doi:10.5194/acp-12-557-2012, 2012. Shin, H. H. and Hong, S.-Y.: Intercomparison of planetary boundary-layer parameterization in the WRF Model for a single day from CASE-99, Boud.-Lay. Meteorol., 139, 261–281, http://dx.doi.org/10.1007/s10546-010-9583-zdoi:10.1007/s10546-010-9583-z, 2011. Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K., Tignor, M., and Miller, H. L. (Eds.): IPCC, 2007: Summary for Policymakers, 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. Sorooshian, A., Feingold, G., Lebsock, M. D., Jiang, H. L., and Stephens, G. L.: On the precipitation susceptibility of clouds to aerosol perturbations, Geophys. Res. Lett., 36, L13803, http://dx.doi.org/10.1029/2009gl038993doi:10.1029/2009gl038993, 2009. Stevens, B.: Bulk boundary-layer concepts for simplified models of tropical dynamics, Theor. Comp. Fluid Dyn., 20, 279–304, http://dx.doi.org/10.1007/S00162-006-0032-Zdoi:10.1007/S00162-006-0032-Z, 2006. Stevens, B. and Feingold, G.: Untangling aerosol effects on clouds and precipitation in a buffered system, Nature, 461, 607–613, http://dx.doi.org/10.1038/nature08281doi:10.1038/nature08281, 2009. Stevens, B., Cotton, W. R., Feingold, G., and Moeng C.-H.: Large-Eddy simulations of strongly precipitating, shallow, stratocumulus-topped boundary layers, J. Atmos. Sci., 55, 3616–3638, 1998. Terai, C. R., Wood, R., Leon, D. C., and Zuidema, P.: Does precipitation susceptibility vary with increasing cloud thickness in marine stratocumulus?, Atmos. Chem. Phys., 12, 4567–4583, http://dx.doi.org/10.5194/acp-12-4567-2012doi:10.5194/acp-12-4567-2012, 2012. Toniazzo, T., Abel, S. J., Wood, R., Mechoso, C. R., Allen, G., and Shaffrey, L. C.: Large-scale and synoptic meteorology in the south-east Pacific during the observations campaign VOCALS-REx in austral Spring 2008, Atmos. Chem. Phys., 11, 4977–5009, http://dx.doi.org/10.5194/acp-11-4977-2011doi:10.5194/acp-11-4977-2011, 2011. Twomey, S.: Influence of Pollution on Shortwave Albedo of Clouds, J. Atmos. Sci., 34, 1149–1152, 1977. Wang, H. and Feingold, G.: Modeling Mesoscale Cellular Structures and Drizzle in Marine Stratocumulus. Part I: Impact of Drizzle on the Formation and Evolution of Open Cells, J. Atmos. Sci., 66, 3237–3256, http://dx.doi.org/10.1175/2009jas3022.1doi:10.1175/2009jas3022.1, 2009a. Wang, H. and Feingold, G.: Modeling Mesoscale Cellular Structures and Drizzle in Marine Stratocumulus. Part II: The Microphysics and Dynamics of the Boundary Region between Open and Closed Cells, J. Atmos. Sci., 66, 3257–3275, http://dx.doi.org/10.1175/2009jas3120.1doi:10.1175/2009jas3120.1, 2009b. Wang, H. and McFarquhar, G. M.: Modeling aerosol effects on shallow cumulus convection under various meteorological conditions observed over the Indian Ocean and implications for development of mass-flux parameterizations for climate models, J. Geophys. Res.-Atmos., 113, D20201, http://dx.doi.org/10.1029/2008jd009914doi:10.1029/2008jd009914, 2008a. Wang, H. and McFarquhar, G. M.: Large-eddy simulations of the diurnal cycle of shallow convection and cloudiness over the tropical Indian Ocean, Q. J. Roy. Meteor. Soc., 134, 643–661, http://dx.doi.org/10.1002/Qj.238doi:10.1002/Qj.238, 2008b. Wang, M., Ghan, S., Ovchinnikov, M., Liu, X., Easter, R., Kassianov, E., Qian, Y., and Morrison, H.: Aerosol indirect effects in a multi-scale aerosol-climate model PNNL-MMF, Atmos. Chem. Phys., 11, 5431–5455, http://dx.doi.org/10.5194/acp-11-5431-2011doi:10.5194/acp-11-5431-2011, 2011. Wang, M., Ghan, S., Liu, X., L'Ecuyer T., Zhang, K., Morrison, H., Ovchinnikov, M., Easter, R., Marchand, R., Chand, D., Qian, Y., and Penner, J.: Constraining cloud lifetime effects of aerosols using A-Train Satellite observations, Geophys. Res. Lett., 39, L15709, http://dx.doi.org/10.1029/2012GL052204doi:10.1029/2012GL052204, 2012. Wood, R.: Cancellation of aerosol indirect effects in marine stratocumulus through cloud thinning, J. Atmos. Sci., 64, 2657–2669, http://dx.doi.org/10.1175/Jas3942.1doi:10.1175/Jas3942.1, 2007. Wood, R., Bretherton, C. S., Leon, D., Clarke, A. D., Zuidema, P., Allen, G., and Coe, H.: An aircraft case study of the spatial transition from closed to open mesoscale cellular convection over the Southeast Pacific, Atmos. Chem. Phys., 11, 2341–2370, http://dx.doi.org/10.5194/acp-11-2341-2011doi:10.5194/acp-11-2341-2011, 2011a. Wood, R., Mechoso, C. R., Bretherton, C. S., Weller, R. A., Huebert, B., Straneo, F., Albrecht, B. A., Coe, H., Allen, G., Vaughan, G., Daum, P., Fairall, C., Chand, D., Gallardo Klenner, L., Garreaud, R., Grados, C., Covert, D. S., Bates, T. S., Krejci, R., Russell, L. M., de Szoeke, S., Brewer, A., Yuter, S. E., Springston, S. R., Chaigneau, A., Toniazzo, T., Minnis, P., Palikonda, R., Abel, S. J., Brown, W. O. J., Williams, S., Fochesatto, J., Brioude, J., and Bower, K. N.: The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations, Atmos. Chem. Phys., 11, 627–654, http://dx.doi.org/10.5194/acp-11-627-2011doi:10.5194/acp-11-627-2011, 2011b. Woodhouse, M. T., Carslaw, K. S., Mann, G. W., Vallina, S. M., Vogt, M., Halloran, P. R., and Boucher, O.: Low sensitivity of cloud condensation nuclei to changes in the sea-air flux of dimethyl-sulphide, Atmos. Chem. Phys., 10, 7545–7559, http://dx.doi.org/10.5194/acp-10-7545-2010doi:10.5194/acp-10-7545-2010, 2010. Yang, M., Blomquist, B. W., and Huebert, B. J.: Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide, Atmos. Chem. Phys., 9, 9225–9236, http://dx.doi.org/10.5194/acp-9-9225-2009doi:10.5194/acp-9-9225-2009, 2009. Yang, M., Huebert, B. J., Blomquist, B. W., Howell, S. G., Shank, L. M., McNaughton, C. S., Clarke, A. D., Hawkins, L. N., Russell, L. M., Covert, D. S., Coffman, D. J., Bates, T. S., Quinn, P. K., Zagorac, N., Bandy, A. R., de Szoeke, S. P., Zuidema, P. D., Tucker, S. C., Brewer, W. A., Benedict, K. B., and Collett, J. L.: Atmospheric sulfur cycling in the southeastern Pacific – longitudinal distribution, vertical profile, and diel variability observed during VOCALS-REx, Atmos. Chem. Phys., 11, 5079–5097, http://dx.doi.org/10.5194/acp-11-5079-2011doi:10.5194/acp-11-5079-2011, 2011. Yang, Q., Gustafson Jr., W. I., Fast, J. D., Wang, H., Easter, R. C., Morrison, H., Lee, Y.-N., Chapman, E. G., Spak, S. N., and Mena-Carrasco, M. A.: Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem, Atmos. Chem. Phys., 11, 11951–11975, http://dx.doi.org/10.5194/acp-11-11951-2011doi:10.5194/acp-11-11951-2011, 2011. Zaveri, R. A., Easter, R. C., Fast, J. D., and Peters, L. K.: Model for Simulating Aerosol Interactions and Chemistry (MOSAIC), J. Geophys. Res.-Atmos., 113, D13204, http://dx.doi.org/10.1029/2007jd008782doi:10.1029/2007jd008782, 2008. Zaveri, R. and Peters, L. K.: A new lumped structure photochemical mechanism for large-scale applications, J. Geophys. Res., 104, 30387–30415, 1999. Zhang, Y., Wen, X. Y., and Jang, C. J.: Simulating chemistry-aerosol-cloud-radiation-climate feedbacks over the continental US using the online-coupled Weather Research Forecasting Model with chemistry (WRF/Chem), Atmos. Environ., 44, 3568–3582, http://dx.doi.org/10.1016/J.Atmosenv.2010.05.056doi:10.1016/J.Atmosenv.2010.05.056, 2010. Zheng, X., Albrecht, B., Jonsson, H. H., Khelif, D., Feingold, G., Minnis, P., Ayers, K., Chuang, P., Donaher, S., Rossiter, D., Ghate, V., Ruiz-Plancarte, J., and Sun-Mack, S.: Observations of the boundary layer, cloud, and aerosol variability in the southeast Pacific near-coastal marine stratocumulus during VOCALS-REx, Atmos. Chem. Phys., 11, 9943–9959, http://dx.doi.org/10.5194/acp-11-9943-2011doi:10.5194/acp-11-9943-2011, 2011. Zuidema, P., Leon, D., Pazmany, A., and Cadeddu, M.: Aircraft millimeter-wave passive sensing of cloud liquid water and water vapor during VOCALS-REx, Atmos. Chem. Phys., 12, 355–369, http://dx.doi.org/10.5194/acp-12-355-2012doi:10.5194/acp-12-355-2012, 2012.