Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 7 6 2007 10.5194/acp-7-1629-2007 http://www.atmos-chem-phys.net/7/1629/2007/ http://www.atmos-chem-phys.net/7/1629/2007/acp-7-1629-2007.html http://www.atmos-chem-phys.net/7/1629/2007/acp-7-1629-2007.pdf 1629 1643 2007-03-27 The global impact of supersaturation in a coupled chemistry-climate model A. Gettelman andrew@ucar.edu D. E. Kinnison National Center for Atmospheric Research, Boulder, CO, USA Ice supersaturation is important for understanding condensation in the upper troposphere. Many general circulation models however do not permit supersaturation. In this study, a coupled chemistry climate model, the Whole Atmosphere Community Climate Model (WACCM), is modified to include supersaturation for the ice phase. Rather than a study of a detailed parameterization of supersaturation, the study is intended as a sensitivity experiment, to understand the potential impact of supersaturation, and of expected changes to stratospheric water vapor, on climate and chemistry. High clouds decrease and water vapor in the stratosphere increases at a similar rate to the prescribed supersaturation (20% supersaturation increases water vapor by nearly 20%). The stratospheric Brewer-Dobson circulation slows at high southern latitudes, consistent with slight changes in temperature likely induced by changes to cloud radiative forcing. The cloud changes also cause an increase in the seasonal cycle of near tropopause temperatures, increasing them in boreal summer over boreal winter. There are also impacts on chemistry, with small increases in ozone in the tropical lower stratosphere driven by enhanced production. The radiative impact of changing water vapor is dominated by the reduction in cloud forcing associated with fewer clouds (~+0.6 Wm^−2) with a small component likely from the radiative effect (greenhouse trapping) of the extra water vapor (~+0.2 Wm^−2), consistent with previous work. Representing supersaturation is thus important, and changes to supersaturation resulting from changes in aerosol loading for example, might have a modest impact on global radiative forcing, mostly through changes to clouds. There is no evidence of a strong impact of water vapor on tropical tropopause temperatures. Andrews, D., Holton, J., and Leovy, C.: Middle Atmosphere Dynamics, Academic Press, New York, 1987. Boville, B A., Rasch, P J., Hack, J J., and McCaa, J R.: Represenation of Clouds and Precipitation in the Community Atmosphere Model Version 3 (CAM3), J. Climate, 19, 2184–2198, 2006. Brasseur, G P., Hauglustaine, D A., Walters, S., Rasch, P J., Muller, J.-F., Granier, C., and Tie, X X.: MOZART, a global chemical transport model for ozone and related chemical tracers 1. Model description, J. Geophys. Res., 103, 28 265–28 289, 1998. Butchart, N. A., Scaife, A., Bourqui, M., de Grandpré, J., Hare, S. H. E., Kettleborough, J., Langematz, U., Manzini, E., Sassi, F., Shibata, K., Shindell, D., and Sigmond, M.: Simulations of anthropogenic change in the strength of the BrewerÐDobson circulation, Clim. Dyn., 27, 727–741, doi:10.1007/s00382-006-0162-4, 2006. Cess, R D.: Water Vapor Feedback in Climate Models, Science, 310, 795–796, 2005. Collins, W D., Rasch, P J., Boville, B A., Hack, J J., McCaa, J R., Williamson, D L., Briegleb, B P., Bitz, C M., Lin, S.-J., and Zhang, M.: The Formulation and Atmospheric Simulation of the Community Atmosphere Model: CAM3, J. Climate, 19, 2122–2161, 2006. Dvortsov, V L. and Solomon, S.: Response of the stratospheric temperatures and ozone to past and future increases in stratospheric humidity, J. Geophys. Res., 106, 7505–7514, 2001. Eyring, V., Butchart, N., Waugh, D. W., et al.: Assessment of temperature, trace species, and ozone in chemistry-climate model simulations of the recent past, J. Geophys. Res., 111, D22308, doi:10.1029/2006JD007327, 2006. Forster, P. M. d F. and Shine, K P.: Assessing the climate impact of trends in stratospheric water vapor, Geophys. Res. Lett., 29(6), 1086, doi:10.1029/2001GL013909, 2002. % Gettelman, A., Forster, P. M. de F., Fujiwara, M., Fu, Q., Vomel, H., Gohar, L. K., Johanson, C., and Ammerman, M.: Radiation balance of the tropical tropopause layer, J. Geophys. Res., 109, D07103, doi:10.1029/2003JD004190, 2004. Gettelman, A., Fetzer, E J., Eldering, A., and Irion, F W.: The Global Distribution of Supersaturation in the Upper Troposphere from the Atmospheric Infrared Sounder, J. Climate, 19(23), 6089–6103, 2006. Gierens, K. and Spichtinger, P.: On the size distribution of ice supersaturation regions in the upper troposphere and lower stratosphere, Ann. Geophys., 18, 499–504, 2000. Holton, J R. and Gettelman, A.: Horizontal transport and dehydration in the stratosphere, Geophys. Res. Lett., 28, 2799–2802, 2001. Holton, J R., Haynes, P H., Douglass, A R., Rood, R B., and Pfister, L.: Stratosphere–Troposphere Exchange, Rev. Geophys., 33, 403–439, 1995. Horowitz, L. W., Walters, S., Mauzerall, D. L., et al.: A global simulation of tropospheric ozone and related tracers: Description and evaluation of MOZART, version 2, J. Geophys. Res., 108(D24), 4784, doi:10.1029/2002JD002853, 2003. Jensen, E., Smith, J. B., Pfister, L., et~al.: Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration, Atmos. Chem. Phys., 5, 851–862, 2005. Jensen, E J., Read, W G., Mergenthaler, J., Sandor, B J., Pfister, L., and Tabazadeh, A.: High humidities and subvisible cirrus near the tropical tropopause, Geophys. Res. Lett., 26, 2347–2350, 1999. Joshi, M., Shine, K., Ponater, M., Stuber, N., Sausen, R., and Li, L.: A comparison of climate response to different radiative forcings in three general circulation models: towards an improved metric of climate change, Clim. Dyn., 20, 843–854, \doi10.1007/s00382-003-0305-9, 2003. Kärcher, B. and Haag, W.: Factors controlling upper tropospheric relative humidity, Ann. Geophys., 22, 705–715, 2004. Kärcher, B. and Lohmann, U.: A parameterization of cirrus cloud formation: Homogenous freezing of supercooled aerosols, J. Geophys. Res., 107(D2), 4010, \doi10.1029/2001JD000470, 2002a. Kärcher, B. and Lohmann, U.: A parameterization of cirrus cloud formation: Homogenous freezing including effects of aerosol size, J. Geophys. Res., 107(D23), 4698, \doi10.1029/2001JD001429, 2002b. Kärcher, B., Hendricks, J., and Lohmann, U.: Physically based parameterization of cirrus cloud formation for use in atmospheric models, J. Geophys. Res., 111, D01205, \doi10.1029/2005JD006219, 2006. % Koop, T., Luo, B., Tsias, A., and Peter, T.: Water activity as the determinant for homogenous ice nucleation in aqueous solutions, Nature, 406, 611–614, 2000. Mote, P. W., Rosenlof, K. H., McIntyre, M. E., et al.: An atmospheric tape recorder: The imprint of tropical tropopause temperatures on stratospheric water vapor, J. Geophys. Res., 101, 3989Ð4006, 1996. Murphy, D M. and Koop, T.: Review of the vapour pressure of ice and supercooled water for atmospheric applications, Quart. J. Roy. Meteorol. Soc., 131, 1539–1565, 2005. Osterman, G B., Salawitch, R J., Sen, B., Toon, G C., Stachnik, R A., Pickett, H M., Margitan, J J., Blavier, J F., and Peterson, D B.: Baloon-borne measurements of stratospheric radicals and their precursors: Implications for the production and loss of ozone, Geophys. Res. Lett., 24, 1107–1110, 1997. Ramanathan, V., Cess, R D., Harrison, E F., Minnis, P., Barkstrom, B R., Ahmad, E., and Hartmann, D.: Cloud-Radiative Forcing and Climate: Results from the Earth Radiation Budget Experiment, Science, 243, 57–63, 1989. Randel, W J., Gettelman, A., Wu, F., Russell III, J M., Zawodny, J., and Oltmans, S.: Seasonal variation of water vapor in the lower stratosphere observed in Halogen Occultation Experiment data, J. Geophys. Res., 106, 14 313–14 325, 2001. Randel, W J., Wu, F., Oltmans, S J., Rosenlof, K., and Nedoluha, G E.: Interannual changes of stratospheric water vapor and correllations with tropical tropopause temperatures, J. Atmos. Sci., 61, 2133–2148, 2004. Rasch, P J. and Kristjansson, J E.: A Comparison of CCM3 Model climate using diagnosed and predicted condensate parameterizations, J. Climate, 11, 1587–1614, 1998. Shindell, D T.: Climate and ozone response to increased stratospheric water vapor, Geophys. Res. Lett., 28, 1551–1554, 2001. Slingo, J M.: The development and verification of a cloud prediction scheme for the ECMWF model, Quart. J. Roy. Meteorol. Soc., 113, 899–927, 1987. SPARC: Assessment of Water Vapor in the Upper Troposphere and Lower Stratosphere, WMO/TD-1043, Stratospheric Processes and Their Role In Climate, World Meteorological Organization, Paris, 2000. Spichtinger, P., Gierens, K., Leiterer, U., and Dier, H.: Ice supersaturation in the tropopause region over Lindenberg, Germany, Meteorologische Zeitschrift, 12, 143–156, 2003a. Spichtinger, P., Gierens, K., and Read, W.: The global distribution of ice-supersaturated regions as seen by the Microwave Limb Sounder, Quart. J. Roy. Meteorol. Soc., 129, 3391–3410, 2003b. Stenke, A. and Grewe, V.: Simulation of stratospheric water vapor trends: impact on stratospheric ozone chemistry, Atmos. Chem. Phys., 5, 1257–1272, 2005. Stuber, N., Ponater, M., and Sausen, R.: Is the climate sensitivity to ozone perturbations enhanced by stratospheric water vapor feedback?, Geophys. Res. Lett., 28, 2887–2890, 2001. Stuber, N., Ponater, M., and Sausen, R.: Why radiative forcing might fail as a predictor of climate change, Clim. Dynamics, 24, 497–510, \doi10.1007/s00382-004-0497-7, 2005. Tompkins, A M., Gierens, K., and Rädel, G.: Ice supersaturation in the ECMWF forecast system, Quart. J. Roy. Meteorol. Soc., in press, 2007. Waugh, D W. and Hall, T M.: Age of Stratospheric Air: Theory, Observations and Models, Rev. Geophys., 40(4), 1–26, 1010, doi:10.1029/2000RG000101, 2002. Wennberg, P O., Cohen, R C., Stimpfle, R M., Koplow, J P., Anderson, J G., Salawitch, R J., Fahey, D W., Woodbridge, E L., Keim, E R., Gao, R S., Webster, C R., May, R D., Toohey, D W., Avallone, L M., Proffitt, M H., Loewenstein, M., Podolske, J R., Chan, K R., and Wofsy, S C.: Removal of Stratospheric O₃ by Radicals: In Situ Measurements of OH, HO₂, NO, NO₂, ClO and BrO, Science, 266, 398–404, 1994.