An investigation into the aerosol dispersion effect through the activation process in marine stratus clouds
OPEN ACCESS
Loading...
Author / Producer
Date
2007-06-16
Publication Type
Journal Article
ETH Bibliography
yes
OPEN ACCESS
Data
Rights / License
Abstract
The aerosol dispersion effect (the influence of an increasing number of aerosol particles on the width of the cloud droplet size distribution) has been observed in maritime clouds [e.g., Liu and Daum, 2002]. Climate model simulations show that the dispersion effect at least partially compensates the first indirect aerosol effect. The application of observational data from maritime stratus/stratocumulus clouds into an adiabatic parcel model allows to analyze the role of the aerosol activation process for the dispersion effect in order to better understand the microphysical mechanism of the dispersion effect in the early stage of cloud formation. When the total aerosol number concentration is increased, the parcel model simulations show that the higher number of aerosol particles at cloud base reduces the supersaturation, which results in a slower particle growth rate, and thus more cloud droplets remain small. This extends the droplet spectra toward the smaller size end and increases the spectral width. The broadening effect partially offsets the reduction of droplet radius because of an enhanced number of aerosol particles, leading to a positive aerosol dispersion effect. Sensitivity studies show that the dispersion effect decreases for increasing updraft velocities. When the updraft velocity approaches 55 m s−1, the dispersion effect almost vanishes for maritime stratus clouds. Aerosols composed of sulfate or of less soluble organics increase the dispersion effect as compared to sea-salt aerosols, whereas condensation of gaseous nitric acid on aerosols decreases the dispersion effect in marine stratus clouds.
Permanent link
Publication status
published
External links
Editor
Book title
Journal / series
Volume
112 (11)
Pages / Article No.
Publisher
American Geophysical Union
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
Aerosol dispersion effect; cloud droplet size distribution; indirect aerosol effect
Organisational unit
03690 - Lohmann, Ulrike / Lohmann, Ulrike