Clouds enhance aerosol warming
doi:10.1038/nindia.2009.56 Published online 23 February 2009
A team of Indo-US researchers has used a satellite-based approach to show that the warming effect of aerosols increases with underlying cloud cover1. The study demonstrates the importance of cloud prediction for the accurate quantification of aerosol direct effects.
The team quantified the direct, top-of-atmosphere radiative effect of aerosol layers advected over the partly cloudy boundary layer of the southeastern Atlantic Ocean. Their experiments were conducted between July and October of 2006 and 2007.
The relationship between the warming effect of aerosols and the underlying cloud coverage is nearly linear, they say, making it possible to define a critical cloud fraction at which the aerosols switch from exerting a net cooling to a net warming effect.
For this region and time period, the critical cloud fraction was found to be about 0.4. This is strongly sensitive to the amount of solar radiation the aerosols absorb and the ratio of reflected to incident light (albedo) of the underlying clouds.
The team estimates that the regional-mean warming effect of aerosols is three times higher when large-scale spatial covariation between cloud cover and aerosols is taken into account.
The authors of this work are from: Department of Atmospheric Science, University of Washington, Seattle,Washington, USA; Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India & NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
- Chand, D. et al. Satellite-derived direct radiative effect of aerosols dependent on cloud cover. Nat. Geosci. doi: 10.1038/NGEO437 (2009)