Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 3 4 2007 10.5194/cpd-3-935-2007 http://www.clim-past-discuss.net/3/935/2007/ http://www.clim-past-discuss.net/3/935/2007/cpd-3-935-2007.html http://www.clim-past-discuss.net/3/935/2007/cpd-3-935-2007.pdf 935 960 2007-07-10 Maintenance of polar stratospheric clouds in a moist stratosphere D. B. Kirk-Davidoff dankd@atmos.umd.edu J.-F. Lamarque University of Maryland, Department of Atmospheric and Oceanic Science, USA National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, Colorado, USA Previous work has shown that polar stratospheric clouds (PSCs) could have acted to substantially warm high latitude regions during past warm climates such as the Eocene (55 Ma). Using a simple model of stratospheric water vapor transport and polar stratospheric cloud (PSC) formation, we investigate the dependence of PSC optical depth on tropopause temperature, cloud microphysical parameters, stratospheric overturning, and tropospheric methane. We show that PSC radiative effects can help slow removal of water from the stratosphere via self-heating. However, we also show that the ability of PSCs to have a substantial impact on climate depends strongly on the PSC particle number density and the strength of the overturning circulation. Thus even a large source of stratospheric water vapor (e.g. from methane oxidation) will not result in substantial PSC radiative effects unless PSC ice crystal number density is high, and stratospheric overturning (which modulates polar stratospheric temperatures) is low. These results are supported by analysis of a series of runs of the NCAR WACCM model with methane concentrations varying up to one thousand times present levels. Brock, C. A., Hamill, P., Wilson, J. C., Jonsson, H. H., and Chan, K. R.: Particle Formation in the Upper Tropical Troposphere: A Source of Nuclei for the Stratospheric Aerosol, Science, 270, 1650–1653, 1995. Chou, M. D., Suarez, M. J., Liang, X. Z., and Yan, M. M. H.: A Thermal Infrared Parameterization for Atmospheric Studies, NASA Technical Memorandum TM104606,19, 2001 Chou, M. D. and Suarez, M. J.: A solar radiation parameterization for atmospheric studies, NASA Technical Memorandum TM-104606, 11, 1999 Drdla, K., Schoeberl, M. R., and Browell, E. V.: Microphysical modeling of the 1999–2000 Arctic winter: 1. Polar stratospheric clouds, denitrification, and dehydration, J. Geophys. Res., 107, 8312–8332, 2002. Fortin, T. J., Drdla, K., Iraci, L. T., and Tolbert, M. A.: Ice condensation on sulfuric acid tetrahydrate: Implications for polar stratospheric clouds, Atmos. Chem. Phys., 3, 987–997, 2003. Huber, M. and Sloan, L. C.: Heat transport, deep waters, and thermal gradients: Coupled simulation of an Eocene Greenhouse Climate, J. Geophys. Res., 28, 3481–3484, 2001. % Jensen, E.J. O.B. Toon,et al.: Prevalence of ice-supersaturated regions in the upper troposphere: Implications for optically thin ice cloud formation, J. Geophys. Res., 106, 17,253–17,266, 2001. Kawamoto, N. and Shiotani, M.: Interannual variability of the vertical descent rate in the Antarctic polar vortex, J. Geophys. Res., 105, 11 935–11 946, 2000. Kirk-Davidoff, D. B and R. S.,: An Energy Balance Model Based on Potential Vorticity Homogenization, J. Climate, 431–448, 2000. Kirk-Davidoff, D. B., Schrag, D. P., and Anderson, J. G.: On the Feedback of Stratospheric Clouds on Polar Climate. Geophys. Res. Let., 29(11), 1556, doi:10.1029/2002GL014659, 2002. Lamarque, J.-F., Kiehl, J., Shields, C,. Boville, B. A., and Kinnison, D. E.: Modeling the response to changes in tropospheric methane concentration: Application to the Permian-Triassic boundary, Paleoceanography, 21, PA3006, doi:10.1029/2006PA001276, 2006. McLinden, C. A., McConnell, J. C., McElroy, C. T., and Griffioen, E.: Observations of Stratospheric Aerosol Using CPFM Polarized Limb Radiances, J. Atmos. Phys., 56, 233–240, 1999. Peter, T.: Microphysics and Heterogeneous Chemistry of Polar Stratospheric Clouds, Annu. Rev. Phys. Chem., 48, 785–822, 1997. Scheele, M. P., Siegmund, P. C., and van Velthoven, P. F. J.: Stratospheric age of air computed with trajectories based on various 3D-Var and 4D-Var data sets, Atmos. Chem. Phys., 5, 1–7, 2005. Sloan, L. C. and Pollard, D.: Polar stratospheric clouds: a high-latitude warming mechanism in an ancient greenhouse world, Geophys. Res. Lett., 25, 3517–3520, 1998.