HR: 11:08h
AN: A32B-04    [Abstracts]
TI: Climatology of Aerosol Radiative Properties Over the Oceans
AU: * Ogren, J A
EM: John.A.Ogren@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway R/CMDL1, Boulder, CO 80305 United States
AU: Ravishankara, I H
EM: Isaac.Ravishankara@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway R/CMDL1, Boulder, CO 80305 United States
AU: McComiskey, A
EM: Allison.Payton@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway R/CMDL1, Boulder, CO 80305 United States
AU: McComiskey, A
EM: Allison.Payton@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado 216 UCB, Boulder, CO 80309 United States
AB: Evaluation of the direct radiative forcing by atmospheric aerosols requires knowledge of both the quantity and the radiative properties of the particles. Quantity is generally described by aerosol optical depth, which can be measured globally from space. Satellite sensors are not well suited for measuring the needed radiative properties of the particles, in particular, the relative amounts of scattering versus absorption and the angular distribution of the scattered light. The single-scattering albedo, defined as the ratio of aerosol scattering coefficient to extinction coefficient, describes the absorptive nature of the particles. The angular scattering properties are described by two different properties, depending on the measurement method: the asymmetry parameter is the average cosine of the scattering angle, and the hemispheric backscatter fraction is the fraction of the light that is scattered back towards the light source. This paper presents the results of a review of measurements of these radiative properties from ground stations, ships, and aircraft over the oceans. Most of the publications come from short-term, intensive field campaigns, with a fairly limited number of observation days. In addition to the survey of 52 published papers, 19 of which reported measurements of the needed radiative properties, two databases of long-term, ground-based measurements of aerosol radiative properties were analyzed to describe seasonal variations at the few oceanic sites where long-term measurements are available. The AERONET database contains results from 9 island or coastal stations with multi-year observations of column-averaged asymmetry parameter, although these sites rarely encounter conditions with sufficient aerosol loadings for determination of single-scattering albedo. The CMDL database contains results from four island or coastal stations with multi-year, in-situ observations at the surface of hemispheric backscatter fraction and single-scattering albedo. The AERONET and CMDL databases contribute a total of nearly 10,000 observation-days towards the climatology, overwhelming the statistical contribution from the roughly 900 observation-days of intensive field campaigns. Intensive field campaigns represent a much larger geographic area than the few locations in the long-term databases. Together, the two types of data sets provide the basis for a measurement-based evaluation of direct radiative forcing. In addition to presenting the climatological averages of the aerosol radiative properties, the paper will discuss the limitations of the current data sets in terms of their spatial and temporal coverage and the adequacy of the parameters that are measured.
DE: 3359 Radiative processes
DE: 3309 Climatology (1620)
DE: 0305 Aerosols and particles (0345, 4801)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting