Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective

Krzysztof M. Markowicz, Piotr J. Flatau, P. K. Quinn, Christian M. Carrico, M. K. Flatau, A. M. Vogelmann, David Bates, M. Liu, Mark J. Rood

Research output: Contribution to journalArticlepeer-review


We present direct radiometric observations of aerosol radiative forcing during the ACE-Asia experiment (March and April of 2001). The observational analysis is based on radiometer data obtained from the NOAA ship Ronald H. Brown, and shipboard measurements of the aerosol chemical and scattering properties are used to construct a model of the aerosol optical properties for use in radiative transfer calculations. The model is validated against the radiometric observations and is used to diagnose the aerosol and environmental factors that contribute to the observed forcings. The mean value of aerosol optical thickness observed during the ACE-Asia cruise over the Sea of Japan was 0.43 (±0.25) at 500 nm, while the single-scattering albedo was 0.95 (±0.03) at ambient relative humidity. We find a large correlation (r2 = 0.69) between single-scattering albedo and relative humidity. Aerosols caused a mean decrease in the diurnally averaged solar radiation of 26.1 W m-2 at the surface, while increasing the atmospheric solar absorption and top of atmosphere reflected solar radiation by 13.4 W m-2 and 12.7 W m-2, respectively. The mean surface aerosol forcing efficiency (forcing per unit optical depth) over the Sea of Japan was -60 W m-2 and is influenced by high values of relative humidity. We show that decreasing the relative humidity to 55% enhances the aerosol forcing efficiency by as much as 6- 10 W m-2. This dependency on relative humidity has implications for comparisons of aerosol forcing efficiencies between different geographical locations.

Original languageEnglish (US)
Pages (from-to)ACE 30-1 - ACE 30-12
JournalJournal of Geophysical Research: Atmospheres
Issue number23
StatePublished - Dec 16 2003


  • ACE-Asia
  • Aerosol
  • Forcing
  • Humidity
  • Optical depth

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology


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