ARM Aerosol IOP May 2003
Schwartz, S.E.(a), Ferrare R.(b), Ogren, J.E.(c), Daum, P.H.(a), Schmid, B.(d), and Ghan, S.(e), Brookhaven National Laboratory (a), NASA Langley Research Center (b), NOAA Climate Monitoring and Diagnostics Laboratory (c), Bay Area Environmental Research (d), Pacific Northwest National Laboratory (e)
Twelfth Atmospheric Radiation Measurement (ARM) Science Team Meeting
Aerosol influences on shortwave radiation are substantial locally and globally. An aerosol optical thickness of 0.1 results in an instantaneous decrease in direct normal surface irradiance of ca 100 watts per square meter, and (depending on particle size and single scattering albedo) a top of atmosphere forcing of ca 30 watts per square meter. Such optical depths are not uncommon at SGP. Aerosols also substantially influence the diffuse downwelling surface irradiance; the magnitude of this influence, and also of the vertical distribution of atmospheric heating, depends sensitively on the aerosol single scattering albedo. Knowledge of pertinent aerosol properties is required to accurately represent aerosol forcing in models. ARM CART has been systematically measuring aerosol properties at the surface and limited measurements aloft from light aircraft. It is shown by lidar and in-situ measurements that much of the aerosol at SGP is aloft, often in layers that are decoupled from the surface, raising question of the representativeness of surface aerosol properties for these calculations. Vertical profiles of aerosol properties are key parameters required for the computation of radiative flux profiles. Detailed measurements of aerosol optical properties are required to characterize the aerosol optical, microphysical, and chemical properties at the surface and above the SGP site for accurately computing radiative fluxes. Such well-characterized data would permit a more detailed evaluation of the performance of radiative transfer models to compute flux profiles and heating rates. The planned IOP will carry out a variety of closure experiments on aerosol optical properties and their radiative influence. Additionally, planned measurements of the aerosol chemical composition size distribution, to be conducted by investigators in the DOE Atmospheric Chemistry Program and Tropospheric Aerosol Program, will allow testing of the ability to reconstruct optical properties from these measurements. Additional effort will be directed toward measurement of cloud condensation nucleus concentration as a function of supersaturation and relating to aerosol composition and size distribution. This relation is central to description of the aerosol indirect effect.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
