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Indirect Influence of Humidity on Atmospheric Spectra Near 4 μm
Author(s) -
Hartmann J.M.,
Armante R.,
Toon G. C.,
Scott N.,
Tran H.,
Crevoisier C.,
Chédin A.,
Capelle V.
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl079582
Subject(s) - atmosphere (unit) , spectral line , humidity , atmospheric sciences , environmental science , atmosphere of earth , physics , meteorology , astronomy
We give the first demonstration that humidity has indirect effects on atmospheric spectra near 4 μm, through the influence of collisions with H 2 O on both the collision‐induced band of N 2 and the wings of the CO 2 lines. This is shown by comparing computed and measured values of atmospheric transmissions and outgoing radiances. The usual assumption that collisions with H 2 O and dry air have equal effect on the N 2 and CO 2 absorptions leads to significantly underestimated absorptions for humid atmospheres. This bias is considerably reduced when the influences of H 2 O on the N 2 and CO 2 contributions to the spectra are taken into account using proper spectroscopic models. This opens perspectives of increased accuracy near 4 μm where the atmosphere is relatively transparent, for astronomical observations of outer objects from ground as well as for retrievals of the Earth land/sea surface temperatures from radiances recorded from space.