Aerosol effects on ice clouds: can the traditional concept of aerosol indirect effects be applied to aerosol-cloud interactions in cirrus clouds? Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA
Received: 19 January 2010 – Published in Atmos. Chem. Phys. Discuss.: 21 April 2010 Abstract. Cirrus clouds cover approximately 20–25% of the globe and thus play an
important role in the Earth's radiation budget. Therefore the effect of
aerosols on cirrus clouds can have a substantial impact on global radiative
forcing if either the ice-water path (IWP) and/or the cloud ice number
concentration (CINC) changes. This study examines the aerosol indirect
effect (AIE) through changes in the CINC and IWP for a cirrus cloud case. We
use a cloud-system resolving model (CSRM) coupled with a double-moment
representation of cloud microphysics. Intensified interactions among CINC,
deposition and dynamics play a critical role in increasing the IWP as
aerosols increase. Increased IWP leads to a smaller change in the outgoing
LW radiation relative to that for the SW radiation for increasing aerosols.
Increased aerosols lead to increased CINC, providing increased surface area
for water vapor deposition. The increased deposition causes depositional
heating which produces stronger updrafts, and leads to the increased IWP.
The conversion of ice crystals to aggregates through autoconversion and
accretion plays a negligible role in the IWP response to aerosols, and the
sedimentation of aggregates is negligible. The sedimentation of ice crystals
plays a more important role in the IWP response to aerosol increases than
the sedimentation of aggregates, but not more than the interactions among
the CINC, deposition and dynamics.
Revised: 18 October 2010 – Accepted: 02 November 2010 – Published: 04 November 2010
Citation: Lee, S. S. and Penner, J. E.: Aerosol effects on ice clouds: can the traditional concept of aerosol indirect effects be applied to aerosol-cloud interactions in cirrus clouds?, Atmos. Chem. Phys., 10, 10345-10358, doi:10.5194/acp-10-10345-2010, 2010.