Aerosol direct radiative effects at the ARM SGP and TWP Sites

Abstract:

The aerosol direct radiative effect (DRE) was estimated at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) and Tropical Western Pacific (TWP) sites first under clear-sky conditions. The NASA Langley Fu-Liou radiative transfer model was used with observed inputs including aerosol vertical extinction profile from the Raman lidar; aerosol spectral optical depth, single-scattering albedo and asymmetry factor from Aerosol Robotic Network (AERONET); temperature and water vapor profiles from radiosondes; and surface shortwave spectral albedo from radiometers. A radiative closure experiment was conducted for clear-sky conditions. The mean differences of modeled and observed surface downwelling shortwave 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 the AOD is 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 W m^-2 (-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. We will also quantify the cloudy-sky aerosol DRE for the transparent and opaque cloud situation. For transparent cloudy-skies, cloud detection and retrieved particulate extinction from the Raman lidar will be utilized. For opaque cloudy-skies, cloud detection and retrieved extinction from the Ka-band ARM Zenith Radar will be utilized. The whole-sky aerosol DRE will then be quantified by combining the aerosol DRE for clear- and cloudy-skies.