HR: 16:20h
AN: A54B-01 INVITED     [Abstracts]
TI: Attenuation of Photosynthetically Active Radiation by Aerosols and Characterization of Aerosol Absorption from AERONET
AU: * Eck, T F
EM: teck@ltpmail.gsfc.nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Holben, B N
EM: bholben@pop900.gsfc.nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Schafer, J S
EM: joel.schafer@gsfc.nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Sinyuk, A
EM: asiniuk@ltpmailx.gsfc.nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Smirnov, A
EM: asmirnov@aeronet.gsfc.nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AU: Slutsker, I
EM: Ilya@ltpmailx.gsfc.nasa.gov
AF: NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States
AB: Accurate knowledge of the intensity of incident photosynthetically active radiation (PAR; 400-700 nm) at the surface is important for understanding possible effects on crop productivity and on the net primary productivity of natural ecosystems. Not only the magnitude of the PAR irradiance but also the distribution of that irradiance into direct and diffuse components can have an effect on photosynthesis. In many regions clouds are the primary attenuator of PAR flux, however in some regions there are significant reductions in PAR irradiance at the surface due to aerosol attenuation. The two primary aerosol optical parameters affecting PAR attenuation are the aerosol optical depth which is related to particulate concentration in the total column, and aerosol absorption which is related to the black carbon concentration for pollution and biomass burning aerosols. Model computations show the magnitude of reduction in PAR irradiance as optical depth increases and as aerosol absorption increases, and the increases in diffuse fraction as aerosol optical depth increases and decreases in diffuse fraction as absorption increases. Examples are shown of the retrieval of aerosol absorption (parameterized by the single scattering albedo) from measurements of irradiance and diffuse fraction in conjunction with spectral aerosol optical depth in the PAR wavelength interval. Since PAR flux reduction by aerosols increases as optical path length increases, there is also the effect of greater attenuation in early morning and late afternoon, possibly reducing the effective photoperiod. We also show aerosol absorption retrievals from the new Version 2.0 AERONET retrievals that are more accurate than Version 1.0 due to better characterization of surface reflectance, providing the basic aerosol characterization needed to estimate cloudless sky PAR fluxes.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0360 Radiation: transmission and scattering
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly