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Evidence for N 2 O ν 3 4.5 μ m non‐local thermodynamic equilibrium emission in the atmosphere
Author(s) -
LópezPuertas M.,
Funke B.,
BermejoPantaleón D.,
von Clarmann T.,
Stiller G. P.,
Grabowski U.,
Höpfner M.
Publication year - 2007
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 - 10.1029/2006gl028539
Subject(s) - radiance , mesosphere , daytime , atmospheric sciences , atmosphere (unit) , stratosphere , radiative transfer , environmental science , altitude (triangle) , radiative equilibrium , physics , thermodynamic equilibrium , meteorology , thermodynamics , optics , geometry , mathematics
We present a clear evidence for N 2 O 4.5 μ m non‐local thermodynamic equilibrium (non‐LTE) emissions in the daylight stratosphere and mesosphere from measurements by the MIPAS experiment on board Envisat. We have used non‐LTE radiative transfer models in order to quantify the magnitude and extent of the non‐LTE deviation of N 2 O(001) in the Earth's atmosphere. The departure from LTE in N 2 O during daytime commences at altitudes around 40–50 km, but have significant effects (10%) on daytime limb radiance down to tangent heights of 20 km. The enhancement increases rapidly with altitude, being 20–80% at 50 km, and reaching factors of 2–8 in the lower mesosphere. This study shows that the enhancement is mainly produced by absorption of solar radiation by N 2 O at 4.5 μ m and by V‐V collisions with N 2 (1). Non‐LTE effects are also significant at nighttime, where LTE calculations overpredict N 2 O radiances by 10–20% at 40–55 km tangent heights.