Aerosol Direct Radiative Effects at the ARM SGP and TWP Sites: Clear Skies

Abstract

Abstract The clear‐sky aerosol direct radiative effect (DRE) was estimated at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) and Tropical Western Pacific (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 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, which are within observational uncertainty. At SGP, the estimated annual mean clear‐sky aerosol DRE is −3.00 W m −2 at the top of atmosphere (TOA) and −6.85 W m −2 at the surface. The strongest aerosol DRE of −4.81 (−10.77) W m −2 at the TOA (surface) are in the summer when AODs are largest. The weakest aerosol DRE of −1.28 (−2.77) W m −2 at the TOA (surface) are in November–January when AODs and single‐scattering albedos are lowest. At TWP, the annual mean clear‐sky DRE is −2.82 W m −2 at the TOA and −10.34 W m −2 at the surface. The strongest aerosol DRE of −5.95 (−22.20) W m −2 at the TOA (surface) are in November (October) due to the biomass burning season’s peak. The weakest aerosol DRE of −0.96 (−4.16) W m −2 at the TOA (surface) are in March (April) when AODs are smallest.