HR: 1340h
AN: A43C-1433    [Abstracts]
TI: The role of Saharan dust in determining the first aerosol indirect effect
AU: * Shao, H
EM: hshao@fsu.edu
AF: Florida State University, Meteorology Department, Tallahassee, FL 32306,
AU: Liu, G
EM: liug@met.fsu.edu
AB: Anthropogenic aerosols acting as cloud condensation nuclei affect Earth's radiative balance indirectly by changing cloud radiative properties. This so-called first aerosol indirect effect (AIE) has a potentially large but poorly quantified cooling effect. In modeling the aerosol indirect forcing, because the aerosol-cloud interaction is not resolved in global climate models (GCMs), cloud droplet number concentration is typically parameterized using an empirical relationship that directly relates droplet number concentration to aerosol number concentration based on the measurements between polluted and clean clouds. It is realized that the first AIE obtained in this way can be contaminated by the coherent variation in the pertinent variables such as cloud liquid water and the degree of entrainment mixing. However, the influence from changes in aerosol properties themselves has not received a deserved attention. Using satellite observations over eastern subtropical oceans, we show that over the north-eastern Atlantic the aerosols properties are distinct from the other regions due to the dust particles originating from Sahara desert. These dust particles may significantly reduce the efficiency of aerosols to act as cloud condensation nuclei. As a result, the locally observed first AIE from this region can be significantly deviated from global mean, even resulting in positive values. Because of the large areal fraction of this region, ignoring the influence from the northern Africa dust particles will underestimate the globally averaged first AIE approximately by half.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 1626 Global climate models (3337, 4928)
DE: 1640 Remote sensing (1855)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting