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Aerosol Radiative Effects: Expected Variations in Optical Depth Spectra and Climate Forcing, with Implications for Closure Experiment StrategiesWe examine measurement strategies for reducing uncertainties in aerosol direct radiative forcing by focused experiments that combine surface, air, and space measurements. Particularly emphasized are closure experiments, which test the degree of agreement among different measurements and calculations of aerosol properties and radiative effects. By combining results from previous measurements of large-scale smokes, volcanic aerosols, and anthropogenic aerosols with models of aerosol evolution, we estimate the spatial and temporal variability in optical depth spectra to be expected in the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX, planned for summer 1996 off the Eastern U.S. seaboard). In particular, we examine the expected changes in the wavelength dependence of optical depth as particles evolve through nucleation, growth by condensation and coagulation, and removal via sedimentation. We then calculate the expected radiative climate forcing (i.e. change in net radiative flux) for typical expected aerosols and measurement conditions (e.g. solar elevations, surface albedos, radiometer altitudes). These calculations use new expressions for flux and albedo changes, which account not only for aerosol absorption, but also for instantaneous solar elevation angles and the dependence of surface albedo on solar elevation. These factors, which are usually ignored or averaged in calculations of global aerosol effects, can have a strong influence on fluxes measured in closure experiments, and hence must be accounted for in calculations if closure is to be convincingly tested. We compare the expected measurement signal to measurement uncertainties expected for various techniques in various conditions. Thereby we derive recommendations for measurement strategies that combine surface, airborne, and spaceborne measurements.
Document ID
20020023598
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Russell, Philip B.
(NASA Ames Research Center Moffett Field, CA United States)
Stowe, L. L.
(Satellite Research Lab. Washington, DC United States)
Hobbs, P. V.
(Washington Univ. Seattle, WA United States)
Podolske, James R.
Date Acquired
August 20, 2013
Publication Date
January 1, 1995
Subject Category
Environment Pollution
Meeting Information
Meeting: 21st General Assembly
Location: Boulder, CO
Country: United States
Start Date: July 2, 1995
End Date: July 14, 1995
Sponsors: International Union of Geodesy and Geophysics
Funding Number(s)
PROJECT: RTOP 229-10-32-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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