Premium
Evidence for CH 4 7.6 μm non‐local thermodynamic equilibrium emission in the mesosphere
Author(s) -
LópezPuertas M.,
Koukouli M. E.,
Funke B.,
GilLópez S.,
Glatthor N.,
Grabowski U.,
von Clarmann T.,
Stiller G. P.
Publication year - 2005
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 - 10.1029/2004gl021641
Subject(s) - radiance , mesosphere , radiative transfer , atmospheric sounding , daytime , atmospheric sciences , environmental science , atmospheric radiative transfer codes , atmosphere (unit) , depth sounding , thermodynamic equilibrium , satellite , altitude (triangle) , stratosphere , physics , remote sensing , meteorology , geology , astronomy , thermodynamics , optics , oceanography , geometry , mathematics
We present unequivocal evidence for CH 4 7.6 μm non‐local thermodynamic equilibrium (non‐LTE) mesospheric emissions as measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment on board the ESA Envisat satellite. We have employed non‐LTE radiative transfer models, already used and validated in studies of other atmospheric gases, in order to quantify the magnitude and extent of the CH 4 non‐LTE deviation in the Earth's atmosphere. The observed daytime enhancement signatures apparent in the measured radiances cannot be attributed to enhanced daytime temperatures and/or CH 4 abundance variations and are reproduced successfully with a dedicated CH 4 non‐LTE radiative transfer model. We conclude that, depending on the upper stratospheric/mesospheric temperature structure, the departure from LTE might commence at an altitude as low as 45 km, reaching limb radiance deviations of 20% at 60 km and quickly rising up to 60% at 70 km, for the 7.6 μm CH 4 lines.