The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean

Yoram J. Kaufman*, Ilan Koren, Lorraine A. Remer, Daniel Rosenfeld, Yinon Rudich

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

528 Scopus citations

Abstract

Clouds developing in a polluted environment tend to have more numerous but smaller droplets. This property may lead to suppression of precipitation and longer cloud lifetime. Absorption of incoming solar radiation by aerosols, however, can reduce the cloud cover. The net aerosol effect on clouds is currently the largest uncertainty in evaluating climate forcing. Using large statistics of 1-km resolution MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data, we study the aerosol effect on shallow water clouds, separately in four regions of the Atlantic Ocean, for June through August 2002: marine aerosol (30°S-20°S), smoke (20°S-5°N), mineral dust (5°N-25°N), and pollution aerosols (30°N-60°N). All four aerosol types affect the cloud droplet size. We also find that the coverage of shallow clouds increases in all of the cases by 0.2-0.4 from clean to polluted, smoky, or dusty conditions. Covariability analysis with meteorological parameters associates most of this change to aerosol, for each of the four regions and 3 months studied. In our opinion, there is low probability that the net aerosol effect can be explained by coincidental, unresolved, changes in meteorological conditions that also accumulate aerosol, or errors in the data, although further in situ measurements and model developments are needed to fully understand the processes. The radiative effect at the top of the atmosphere incurred by the aerosol effect on the shallow clouds and solar radiation is -11 ± 3 W/m2 for the 3 months studied; 2/3 of it is due to the aerosol-induced cloud changes, and 1/3 is due to aerosol direct radiative effect.

Original languageEnglish
Pages (from-to)11207-11212
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume102
Issue number32
DOIs
StatePublished - 9 Aug 2005

Keywords

  • Air quality
  • Cloud cover
  • Cloud height
  • Indirect effect
  • Radiative forcing

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