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Aerosol-Induced Changes of Convective Cloud Anvils Produce Strong Climate WarmingThe effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. Small human-induced perturbations to cloud characteristics via aerosol pathways can create a change in the top-of-atmosphere radiative forcing of hundreds of Wm(exp-2) . Here we focus on links between aerosol and deep convective clouds of the Atlantic and Pacific Intertropical Convergence Zones, noting that the aerosol environment in each region is entirely different. The tops of these vertically developed clouds consisting of mostly ice can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing. We find that increased aerosol loading is associated with taller cloud towers and anvils. The taller clouds reach levels of enhanced wind speeds that act to spread and thin the anvi1 clouds, increasing areal coverage and decreasing cloud optical depth. The radiative effect of this transition is to create a positive radiative forcing (warming) at top-of-atmosphere. Furthermore we introduce the cloud optical depth (r), cloud height (Z) forcing space and show that underestimation of radiative forcing is likely to occur in cases of non homogenous clouds. Specifically, the mean radiative forcing of towers and anvils in the same scene can be several times greater than simply calculating the forcing from the mean cloud optical depth in the scene. Limitations of the method are discussed, alternative sources of aerosol loading are tested and meteorological variance is restricted, but the trend of taller clouds; increased and thinner anvils associated with increased aerosol loading remains robust through all the different tests and perturbations.
Document ID
20110014280
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Koren, I.
(Weizmann Inst. of Science Rehovot, Israel)
Remer, L. A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Altaratz, O.
(Weizmann Inst. of Science Rehovot, Israel)
Martins, J. V.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Davidi, A.
(Weizmann Inst. of Science Rehovot, Israel)
Date Acquired
August 25, 2013
Publication Date
May 31, 2010
Publication Information
Publication: Atmospheric Chemistry and Physics
Publisher: Copernicus Publications
Volume: 10
Subject Category
Meteorology And Climatology
Distribution Limits
Public
Copyright
Public Use Permitted.
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