Premium
Subthermal nitric oxide spin‐orbit distributions in the thermosphere
Author(s) -
Lipson S. J.,
Armstrong P. S.,
Dodd J. A.,
Lowell J. R.,
Blumberg W. A. M.,
Nadile R. M.
Publication year - 1994
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 - 10.1029/94gl02450
Subject(s) - thermosphere , population , physics , atmosphere (unit) , orbit (dynamics) , kinetic energy , computational physics , thermodynamics , classical mechanics , ionosphere , demography , astronomy , sociology , engineering , aerospace engineering
The two NO( X ²Π, υ=1, Ω=1/2,3/2) spin‐orbit populations in the Earth's thermosphere have been found to depart by more than a factor of 2 from the ratio expected from thermal equilibrium. The effective temperature describing the observed population distribution is as much as 700 K lower than the local kinetic temperature. Absolute NO(υ=1, J , Ω) column densities were derived from high‐resolution (1 cm −1 ) infrared earthlimb spectra for tangent altitudes up to 200 km, obtained in the CIRRIS 1A Space Shuttle experiment. Nonlinear least‐squares synthetic spectral fitting was used to analyze the NO Δυ=1 fundamental band emissions near 5.3 µm. The spin‐orbit distribution represents a third degree of freedom, along with vibration and rotation, that is not in equilibrium with the local kinetic temperature. These observations may significantly impact the interpretation of band‐integrated measurements of NO in the upper atmosphere, for which equilibrium sublevel distributions have been assumed. The subthermal distribution is most likely produced in the collisional uppumping of NO(υ=0) by O atoms, which is the major source of NO(υ=1) in the thermosphere. This inference suggests that the present effect is related to the subthermal spin‐orbit distributions observed in laboratory studies of NO 2 photodissociation.