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Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol in Situ and Remote Sensing Measurements During TARFOXThe largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the "effective" aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar-derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS-6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study provides, for the first time, a complete set of vertically resolved aerosol size distribution and refractive index data. yielding the vertical distribution of aerosol optical properties required for the determination of aerosol-induced radiative flux changes.
Document ID
20000052523
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Redemann, J.
(Bay Area Environmental Research Inst. San Francisco, CA United States)
Turco, R. P.
(California Univ. Los Angeles, CA United States)
Liou, K. N.
(California Univ. Los Angeles, CA United States)
Russell, P. B.
(NASA Ames Research Center Moffett Field, CA United States)
Bergstrom, R. W.
(Bay Area Environmental Research Inst. San Francisco, CA United States)
Schmid, B.
(Bay Area Environmental Research Inst. San Francisco, CA United States)
Livingston, J. M.
(NASA Langley Research Center Hampton, VA United States)
Hobbs, P. V.
(NASA Ames Research Center Moffett Field, CA United States)
Hartley, W. S.
(NASA Ames Research Center Moffett Field, CA United States)
Ismail, S.
(NASA Langley Research Center Hampton, VA United States)
Ferrare, R. A.
(NASA Langley Research Center Hampton, VA United States)
Browell, E. V.
(NASA Langley Research Center Hampton, VA United States)
Date Acquired
August 19, 2013
Publication Date
February 28, 2000
Publication Information
Publication: Analysis of Atmospheric Aerosol Data Sets and Application of Radiative Transfer Models to Compute Aerosol Effects
Subject Category
Environment Pollution
Report/Patent Number
Paper 1999JD901044
Distribution Limits
Public
Copyright
Other

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