HR: 11:34h
AN: A22D-05    [Abstracts]
TI: What does the common metric of the first aerosol indirect effect really measure?
AU: * Liu, Y
EM: lyg@bnl.gov
AF: Brookhaven National Laboratory, Bldg. 815E, Upton, NY 11973, United States
AU: Daum, P H
EM: phdaum@bnl.gov
AF: Brookhaven National Laboratory, Bldg. 815E, Upton, NY 11973, United States
AB: The central point of the first aerosol indirect effect is that an increase in aerosol number concentration will increase droplet concentration, reduce effective radius (re), and enhance cloud albedo. Therefore, a good measure of the aerosol indirect effect should quantify the effect resulting from aerosol number concentration. In observation of the first aerosol indirect effect, a commonly used measure is the relative change of effective radius (re) with aerosol number concentration (Na): I = dln(re)/dln(Na). In this work, we show that although aerosol number concentration appears to be considered explicitly in this metric, the log operation minimizes the effect from aerosol number concentration. This metric actually measures a sum of two dispersion effects: effect on clouds of the relative dispersion of the pre-cloud aerosol size distribution, and the aerosol effect on the relative dispersion of the cloud droplet size distribution. We further show that a complete characterization of the first aerosol indirect effect requires at least three aerosol quantities: number concentration, mass concentration, and relative dispersion of the aerosol size distribution. Therefore, if resources are available, it is desirable to have one metric or several metrics that completely encompass the effects from all the three quantities.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0321 Cloud/radiation interaction
DE: 0399 General or miscellaneous
DE: 1655 Water cycles (1836)
DE: 4908 Albedo
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting