Observational evidence of a change in radiative forcing due to the indirect aerosol effect

Joyce E. Penner, Xiquan Dong, Yang Chen

Research output: Contribution to journalArticle

141 Scopus citations

Abstract

Anthropogenic aerosols enhance cloud reflectivity by increasing the number concentration of cloud droplets, leading to a cooling effect on climate known as the indirect aerosol effect. Observational support for this effect is based mainly on evidence that aerosol number concentrations are connected with droplet concentrations, but it has been difficult to determine the impact of these indirect effects on radiative forcing. Here we provide observational evidence for a substantial alteration of radiative fluxes due to the indirect aerosol effect. We examine the effect of aerosols on cloud optical properties using measurements of aerosol and cloud properties at two North American sites that span polluted and clean conditions-a continental site in Oklahoma with high aerosol concentrations, and an Arctic site in Alaska with low aerosol concentrations. We determine the cloud optical depth required to fit the observed shortwave downward surface radiation. We then use a cloud parcel model to simulate the cloud optical depth from observed aerosol properties due to the indirect aerosol effect. From the good agreement between the simulated indirect aerosol effect and observed surface radiation, we conclude that the indirect aerosol effect has a significant influence on radiative fluxes.

Original languageEnglish (US)
Pages (from-to)231-234
Number of pages4
JournalNature
Volume427
Issue number6971
DOIs
StatePublished - Jan 15 2004
Externally publishedYes

ASJC Scopus subject areas

  • General

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