Atmos. Chem. Phys. Discuss., 10, 23381-23402, 2010
www.atmos-chem-phys-discuss.net/10/23381/2010/
doi:10.5194/acpd-10-23381-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Anthropogenic aerosols may have increased upper tropospheric humidity in the 20th century
M. Bister and M. Kulmala
Department of Physics, University of Helsinki, Helsinki, Finland

Abstract. Recent simulations of deep convection with a spectral microphysics cloud model show that an increase in aerosol concentration can have a significant effect on the nature of convection with more ice precipitation and less warm rain in polluted air. The cloud lifetime and the area covered by cloud anvils of deep convection are also larger in polluted air. Therefore, it is possible that the increase of anthropogenic aerosols in most of the 20th century has increased humidity and perhaps also cloudiness in the mid- to upper troposphere. Satellite data of upper tropospheric relative humidity in 1979–1997 and observed changes in cloudiness support this hypothesis. As changes in the upper tropospheric humidity strongly affect longwave radiation, it is possible that anthropogenic aerosols have had a significant warming effect in addition to their other known effects on radiation.

Citation: Bister, M. and Kulmala, M.: Anthropogenic aerosols may have increased upper tropospheric humidity in the 20th century, Atmos. Chem. Phys. Discuss., 10, 23381-23402, doi:10.5194/acpd-10-23381-2010, 2010.
 
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