HR: 1340h
AN: A23C-0823    [Abstracts]
TI: Importance of Spectral Shape in Cloud Parameterizations and Indirect Aerosol Effects
AU: * Liu, Y
EM: lyg@bnl.gov
AF: Brookhaven National Laboratory, Bldg. 815, Upton, NY 11973 United States
AU: Daum, P H
EM: phdaum@bnl.gov
AF: Brookhaven National Laboratory, Bldg. 815, Upton, NY 11973 United States
AB: This work expands on our previous studies on the role that the relative dispersion of the cloud droplet size distribution has in improving cloud parameterizations and evaluating indirect aerosol effects. First we demonstrate the importance of the spectral shape in determining cloud radiative properties. Then we show that the relative dispersion changes when aerosol properties change. Especially, we present more observational evidence that an increase in the droplet concentration caused by increased aerosol loading results in an increase in the relative dispersion, leading to a dispersion effect that offsets the Twomey effect. The dispersion effect is further parameterized as a power-law function of the ratio of the liquid water content to the droplet concentration, leading to a new formalism that generalizes the commonly used equations in studies of cloud parameterizations and indirect aerosol effects. It is found that the dispersion effect significantly offsets the Twomey effect, and increases proportionally with the Twomey effect in magnitude. These results suggest that consideration of the dispersion effect, which has been largely ignored, (partially) resolves two fundamental problems confounding the study of indirect aerosol effects: the discrepancies between observations and those expected from the Twomey effect, and the large uncertainty in estimates of indirect aerosol effects. The effects of drizzle mode on the spectral shape and hence on the parameterization of cloud radiative properties are also discussed.
DE: 4801 Aerosols (0305)
DE: 1610 Atmosphere (0315, 0325)
DE: 1655 Water cycles (1836)
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting