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Comment Response 7-1 7 0 0 0 0 a Novel and Correct Attempt to Address Clouds and Aerosols Together

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Comment Response 7-1 7 0 0 0 0 a Novel and Correct Attempt to Address Clouds and Aerosols Together Expert and Government Review Comments on the IPCC WGI AR5 Second Order Draft – Chapter 7 Comment Chapter From From To To No Page Line Page Line Comment Response 7-1 7 0 0 0 0 A novel and correct attempt to address clouds and aerosols together. In general, the chapter is well-written Noted, no action needed. and up-to-date. There still is some scope to improve the document. My suggestions to follow, basically focus on South Asian region [K KRISHNA MOORTHY, INDIA] 7-2 7 0 0 0 0 Overall I found this to be an impressive chapter, covering many key topics in climate science, for both Noted. Individual comments will be addressed below. feedbacks and forcing. As I will note below, there were a few places where I felt that the reasoning in reaching The semi-direct belongs to AFari as it is initially particular conclusions was not compelling and either the evidence needs to be better presented or the caused by the impact of aerosols on radiation. It can conclusion modified. I also query the chapter title. I did not expect to find information on either the water of course interact with aci. vapour feedback or precipitation in this chapter. On another wider issue, I believe that the ari and aci split generally works well and is a helpful advance, but I think there is really some haziness about where the semi- direct should fall - I think this should be acknowledged [Keith Shine, United Kingdom of Great Britain and Northern Ireland] 7-3 7 0 0 0 0 Better links and more consistency between Chapter 6, specifically Section 6.5.4 and Chapter 7, specifically Taken into account. We have added cross-references Section 7.7.3 would improve the quality of both sections and chapters. [Naomi Vaughan, United Kingdom ] to chapter 6 in the introduction of Section 7.7 and FAQ7.3. FAQ7.3 has been rewritten together with Chapter 6 LA and CLAs. 7-4 7 0 0 I commend the authors on putting together a thorough and well-written summary and review of the role of Noted, specific comments will be addressed below. clouds and aerosols in climate and climate change, especially given the challenge of this task. In particular, I like the use of “radiative forcing due to aerosol-cloud interactions”, RFaci, and “adjusted forcing due to cloud- aerosol interactions”, AFaci, to describe the effects of aerosol-cloud-radiation interactions. In my opinion this is much better than trying to analyze specific effects in isolation as has been done frequently in the past, since as stated on p. 7-35 there is evidence for significant interaction and compensation between effects. However, I think this nomenclature is confusing in a few places; specific instances of this are noted below. The authors have also done a very good job highlighting the distinction between aerosol influences on individual clouds, versus the aerosol-cloud-precipitation system as a whole (e.g., lines 16-21 on p. 7-4 of the Executive Summary). I also appreciate the authors’ focus on how effects vary in different regimes (lines 48-52 on p. 7-40 state this point very nicely), and how this diversity of interactions and underlying complexity has important consequences for modeling overall global-scale effects. I think the regime-dependent context could be emphasized even further; specific suggestions are given in comments below. Several other specific minor comments are also detailed below. Finally, while I have read through the entire chapter, most of my comments focus on section 7.4 since this is the section I was specifically asked to review. Nonetheless, I do have several comments pertaining to other sections as well, including the figures. [Hugh Morrison, United States] 7-5 7 0 0 Reference list for comments: Bogegnschutz, P. A., A. Gettelman, H. Morrison, V. E. Larson, D. P. Schanen, N. Noted, specific comments will be addressed below R. Meyer, and C. Craig, 2012: Unified parameterization of the planetary boundary layer and shallow and references will be considered. convection with a higher-order turbulence closure in the Community Atmosphere Model: Single column experiments. Geosci. Model Dev., 5, 1407-1423. de Boer, G., H. Morrison, M. D. Shupe, and R. Hildner, 2011: Evidence of liquid dependent ice nucleation in high-latitude stratiform clouds from surface remote sensors. Geophys. Res. Lett., 38, L01803, doi:10.1029/2010GL046016. Fan, J., L. R. Leung, Z. Li, H. Morrison, Y. Qian, Y. Zhou, and H. Chen, 2012: Aerosol impacts on clouds and precipitation in southeast China - Results from bin and bulk microphysics for the 2008 AMF-China field campaign. J. Geophys. Res., 117, D00K36, doi:10.1029/2011JD016537. Golaz, J.-C., Larson, V. E., and Cotton, W. R.: A pdf-based model for boundary layer clouds part I: method and model descrip- tion, J. Atmos. Sci., 59, 3540–3551, 2002. Grabowski, W. W.: Indirect impact of atmospheric aerosols in idealized simulations of convective-radiative equilibrium, J. Climate, 19, 4664-4682, 2006. Guo, H., Golaz, J.-C., Donner, L. J., Larson, V. E., Schanen, D. P., and Griffin, B. M.: Multi-variate probability density func- tions with dynamics for cloud droplet activation in large-scale models: single column tests, Geosci. Model Dev., 3, 475–486, doi:10.5194/gmd-3-475-2010, 2010. Hill, A. A., G. Feingold, and H. Jiang, 2009: The influence of entrainment and mixing assumption on aerosol- cloud interactions in marine stratocumulus. J. Atmos. Sci., 66, 1450-1464. Khairoutdinov, M., and Kogan, Y., 2000. A new cloud physics parameterization in a large-ddy simulation Do not Cite, Quote or Distribute Page 1 of 190 Expert and Government Review Comments on the IPCC WGI AR5 Second Order Draft – Chapter 7 Comment Chapter From From To To No Page Line Page Line Comment Response model of marine stratocumulus. Monthly Weather Review, 128(1): 229-243. Larson, V. E., and B. M. Griffin, 2012: Analytic upscaling of a local microphysics scheme. Part I: Derivation, Quart. J. Roy. Meteor. Soc., DOI: 10.1002/qj.1967. (in press, available through early online release) Lebo, Z. J., and Seinfold, J. H.: Theoretical basis for convective invigoration due to increased aerosol concentration, Atmos. Chem. Phys., 11, 5407-5429, 2011. Lohmann, U., 2008. Global anthropogenic aerosol effects on convective clouds in ECHAM5-HAM. Atmospheric Chemistry and Physics, 8: 2115-2131. Morrison, H., and W. W. Grabowski, 2011: Cloud system-resolving model simulations of aerosol indirect effects on tropical deep convection and its thermodynamic environment. Atmos. Chem. Phys., 11, 10503- 10523, doi:10.5194/acp-11-10503-2011. Posselt, R., and Lohmann, U., 2009. Sensitivity of the total anthropogenic aerosol effect to the treatment of rain in a global climate model. Geophysical Research Letters, 36: L02805. Slawinska, J., W. W. Grabowski, H. Pawlowska, and H. Morrison, 2012: Droplet activation and mixing in large- eddy simulation of a shallow cumulus field. J. Atmos. Sci., 69, 444-462. van den Heever, S. C., G. L. Stephens, and N. B. Wood, 2011: Aerosol indirect effects on tropical convective characteristics under conditions of radiative-convective equilibrium. J. Atmos. Sci., 68, 699-718. Wang, M., S. Ghan, M. Ovchinnikov, X. Liu, R. Easter, E. Kassianov, Y. Qian, and H. Morrison, 2011: Aerosol indirect effects in a multi-scale aerosol-climate model PNNL-MMF. Atmos. Phys. Chem., 11, 5431-5455, doi:10.5194/acp-11-5431-2011. Wang, M., S. Ghan, X. Liu, T. L’Ecuyer, Kai Zhang, H. Morrison, M. Ovchinnikov, R. Easter, R. Marchand, D. Chand, Y. Qian, and J. E. Penner, 2012: Constraining cloud lifetime effects of aerosols using A-Train satellite observations. Geophys. Res. Lett., 39, L15709, doi:10.1029/2012GL052204, 7 pp. Yang, Q., W. I. Gustafson, Jr., J. D. Fast, H. Wang, R. C. Easter, M. Wang, S. J. Ghan, L. K. Berg, L. R. Leung, and H. Morrison, 2012: Impact of natural and anthropogenic aerosols on marine stratocumulus and precipitation in the Southeast Pacific: A regional modeling study using WRF-Chem. Atmos. Chem. Phys., 12, 8777-8796. [Hugh Morrison, United States] 7-6 7 0 1 Consistency in assessment numbers: Because chapter assessments continue to be refined, please check Noted. Errors in the numbering of Tables were carefully all values (and the uncertainty ranges) carefully between tables, figures, main text, and summary text introduced by the TSU when handling the SOD. within your chapter. If numbers are taken from other chapters, please also ensure the latest results are used. Specific examples will be highlighted in our chapter comments. [Thomas Stocker/ WGI TSU, Switzerland] 7-7 7 0 2 Treatment of Uncertainty: please follow the IPCC guidance note carefully; use italics to highlight formal likelihood statements have been edited for uncertainty assessments; use likelihood in conjunction with high/very high confidence only (except in consistency or removed within the chapter in exceptional cases); if likelihood is given for situations where confidence is less than 'high', we recommend to agreement with IPCC guidance note. put confidence in brackets at the end of the sentence rather than combining both confidence and likelihood in text. Please note - usage of the formal terms from the uncertainty guidance note, (egg. "likely", "confidence" etc) should be restricted to the use within statements which report assessment findings. [Thomas Stocker/ WGI TSU, Switzerland] 7-8 7 0 3 Format of Executive Summary (ES): As agreed at the third lead author meeting, we would ask that all chapters Noted. follow a consistent style for the ES. 1) The first sentence (or two) of each paragraph should be bolded to highlight the key message, with the subsequent sentences providing the detailed quantitative assessment. 2) Statements should incorporate the IPCC Uncertainty Language 3) Each paragraph must include a traceability to the underlying sections/subsections where the key message was drawn from (to the second level section heading), indicated using square brackets at the end of each paragraph.
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