HR: 0800h
AN: A11A-0033    [Abstracts]
TI: The Role of Adiabaticity in the Aerosol First Indirect Effect
AU: * Kim, B
EM: bgk@kangnung.ac.kr
AF: Department of Atmospheric Environmental Sciences Kangnung National University, 123, Jibyundong, Gangnung, 210-702, Korea, Republic of
AU: Miller, M A
EM: miller@bnl.gov
AF: Environmental Sciences Department, Brookhaven National Laboratory, Upton, Upton, NY 11973, United States
AU: Schwartz, S E
EM: ses@bnl.gov
AF: Environmental Sciences Department, Brookhaven National Laboratory, Upton, Upton, NY 11973, United States
AU: Liu, Y
EM: lyg@bnl.gov
AF: Environmental Sciences Department, Brookhaven National Laboratory, Upton, Upton, NY 11973, United States
AU: Min, Q
EM: min@asrc.cestm.albany.edu
AF: Atmospheric Science Research Center, State University of New York at Albany, 251 Fuller Road, Albany, NY 12203, United States
AB: Aerosol indirect effects are the most uncertain of the climate forcing mechanisms that have operated through the industrial period. Several studies have demonstrated modifications of cloud properties due to aerosols and corresponding changes in shortwave and longwave radiative fluxes under specific cloud conditions, but some recent studies have indicated that cloud dynamical processes such as entrainment-mixing may be the primary modulator of cloud optical properties in certain situations. For example, day-to-day variations of the cloud drop effective radius determined from the ground-based remote sensing at the Southern Great Plains were found to be weakly associated with the variations in aerosol loading as characterized by its light-scattering coefficient at the surface, implying that other processes were impacting the cloud radiative properties. To study these other impacts, we extend a previous study to investigate the role of changes in liquid water path (LWP) and the effective radius in single layer stratiform clouds that are induced by entrainment-mixing processes and their effects on cloud radiative properties. We quantify the degree of entrainment-mixing in terms of the adiabaticity defined as the ratio of the observed cloud liquid water path to the corresponding adiabatic value. The cloud optical depth is, as expected, governed primarily by LWP, but that adiabaticity is the next most influential factor. In contrast, the effective radius is found to be equally sensitive to adiabaticity and LWP. In adiabatic clouds the aerosol first indirect effect is clearly observed and related to independent measures of aerosol loading. In sub-adiabatic clouds the aerosol first indirect effect is not readily observed; this may in some circumstances be due to interference from heterogeneous mixing processes that change the droplet number density in a manner that attenuates the effect.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting