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A new spherical model for computing the radiation field available for photolysis and heating at twilightAccurate computation of atmospheric photodissociation and heating rates is needed in photochemical models. These quantities are proportional to the mean intensity of the solar radiation penetrating to various levels in the atmosphere. For large solar zenith angles a solution of the radiative transfer equation valid for a spherical atmosphere is required in order to obtain accurate values of the mean intensity. Such a solution based on a perturbation technique combined with the discrete ordinate method is presented. Mean intensity calculations are carried out for various solar zenith angles. These results are compared with calculations from a plane parallel radiative transfer model in order to assess the importance of using correct geometry around sunrise and sunset. This comparison shows, in agreement with previous investigations, that for solar zenith angles less than 90 deg adequate solutions are obtained for plane parallel geometry as long as spherical geometry is used to compute the direct beam attenuation; but for solar zenith angles greater than 90 deg this pseudospherical plane parallel approximation overstimates the mean intensity.
Document ID
19910047040
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Dahlback, Arne
(Norwegian Institute for Air Research Lillestrom, Norway)
Stamnes, Knut
(Alaska, University Fairbanks, United States)
Date Acquired
August 14, 2013
Publication Date
May 1, 1991
Publication Information
Publication: Planetary and Space Science
Volume: 39
ISSN: 0032-0633
Subject Category
Geophysics
Accession Number
91A31663
Funding Number(s)
CONTRACT_GRANT: NSF DPP-88-16298
CONTRACT_GRANT: NAGW-2165
Distribution Limits
Public
Copyright
Other

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