Aerosol direct radiative effects at the ARM SGP and TWP sites: Clear skies
Fu, Qiang — University of Washington
Area of research
The objective of this project is to examine and quantify aerosol direct radiative effects (DREs) and associated uncertainties at the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility's Southern Great Plains (SGP) and Tropical Western Pacific (TWP) sites under all sky conditions by taking advantage of the advanced ARM long-term comprehensive measurements of aerosol, cloud, radiation, and atmospheric state. This paper reports the aerosol DREs and associated uncertainties at the DOE ARM SGP and TWP sites under clear-sky conditions, as the first step.
The estimated aerosol DREs provide a references to validate the satellite- and model-derived aerosol DREs.
The clear-sky aerosol DRE was estimated at the ARM SGP and TWP sites. The NASA Langley Fu-Liou radiation model was used with observed inputs including aerosol vertical extinction profile from the Raman lidar; spectral aerosol optical depth (AOD), single-scattering albedo and asymmetry factor from the Aerosol Robotic Network; temperature and water vapor profiles from radiosondes; and surface shortwave (SW) spectral albedo from radiometers. A radiative closure experiment was conducted for clear-sky conditions. The mean differences of modeled and observed surface downwelling SW total fluxes were 1 W m−2 at SGP and 2 W m−2 at TWP. At SGP, the estimated annual mean clear-sky aerosol DRE is −3.0±0.6 W m−2 at the top of atmosphere (TOA) and −6.9±1.0 W m−2 at the surface. At TWP, the annual mean clear-sky DRE is −2.8±0.7 W m−2 at the TOA and −10.3±1.3 W m−2 at the surface. The estimated uncertainties in aerosol DREs are mainly caused by the measurement uncertainties in aerosol single-scattering albedo.