Open AccessEvaluation of the aerosol indirect effect in marine stratocumulus clouds: Droplet number, size, liquid water path, and radiative impact
Author(s) -
Twohy Cynthia H.,
Petters Markus D.,
Snider Jefferson R.,
Stevens Bjorn,
Tahnk William,
Wetzel Melanie,
Russell Lynn,
Burnet Frédéric
Publication year - 2005
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2004jd005116
Subject(s) - liquid water path , liquid water content , aerosol , drizzle , atmospheric sciences , marine stratocumulus , environmental science , radiative transfer , particle (ecology) , effective radius , albedo (alchemy) , particle size , cloud physics , particle number , meteorology , cloud computing , physics , chemistry , optics , geology , astrophysics , thermodynamics , volume (thermodynamics) , precipitation , art , galaxy , oceanography , computer science , operating system , art history , performance art
Data from nine stratocumulus clouds in the northeastern Pacific Ocean were analyzed to determine the effect of aerosol particles on cloud microphysical and radiative properties. Seven nighttime and two daytime cases were included. The number concentration of below‐cloud aerosol particles (>0.10 μm diameter) was highly correlated with cloud droplet number concentration. Droplet number concentrations were typically about 75% of particle number concentration in the range of particle concentrations studied (≤400 cm −3 ). Particle number was anticorrelated with droplet size and with liquid water content in drizzle‐sized drops. Radiative impact also depends upon cloud liquid water content and geometric thickness. Although most variability in these macroscopic properties of the clouds could be attributed to variability in the large‐scale environment, a weak anticorrelation between particle concentration and cloud geometric thickness was observed. Because of these variations, no correlation between calculated cloud optical thickness or albedo and particle concentration was detectable for the data set as a whole. For regions with comparable liquid water contents in an individual cloud, higher particle concentrations did correspond to increased cloud optical thickness. These results verify that higher particle concentrations do directly affect the microphysics of stratiform clouds. However, the constant liquid water path assumption usually invoked in the Twomey aerosol indirect effect may not be valid.