Detailed spectroscopic analysis of hydroxyl fundamental vibration‐rotation and pure rotation emission lines has yielded OH(υ,N) absolute column densities for nighttime earthlimb spectra in the 20 to 110‐km tangent height region. High‐resolution spectra were obtained in the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) experiment. Rotationally thermalized populations in υ = 1–9 have been derived from the fundamental bands between 2000 and 4000 cm−1. Highly rotationally excited populations with N ≤ 33 ( ≤ 2.3 eV rotational energy) have been inferred from the pure rotation spectra between 400 and 1000 cm−1. These emissions originate in the airglow region near 85–90 km altitude. Spectral fits of the pure rotation lines imply equal populations in the spinrotation states F1 and F2 but a ratio Π(A′):Π(A″) = 1.8±0.3 for the Λ‐doublet populations. A forward predicting, first‐principles kinetic model has been developed for the resultant OH(υ,N) limb column densities. The kinetic model incorporates a necessary and sufficient number of processes known to generate and quench OH(υ,N) in the mesopause region and includes recently calculated vibration‐rotation Einstein coefficients for the high‐N levels. The model reproduces both the thermal and the highly rotationally excited OH(υ,N) column densities. The tangent height dependence of the rotationally excited OH(υ,N) column densities is consistent with two possible formation mechanisms: (1) transfer of vibrational to rotational energy induced by collisions with O atoms or (2) direct chemical production via H + O3 → OH(υ,N) + O2.

A recursive algorithm was developed to invert spectrally resolved earth limb radiance profiles representing the non‐local thermodynamic equilibrium altitude regime and species/tangent heights that are optically thin. It was used to infer vertical distributions of temperature and excited NO density from data measured by the Spectral Infrared Rocket Experiment in the NO fundamental band near 5.3 µm. The solution for excited NO density was used to compute atmospheric cooling rates for the 5.3‐µm band and the de‐excitation rate constant ko for the reaction NO* + O → NO + O.

A Spectral Infrared Rocket Experiment was launched from Poker Flat, Alaska, on September 28, 1977, to measure infrared emission spectra from the earth limb atmosphere. Spectrometers measured emission spectra from 1.40 to 16.5 µm during 12 vertical scans of the limb region (tangent heights 0 to 250 km) traversing the night, terminator, and day sectors of the limb atmosphere. The spectrometers were cryogenically cooled and telescoped for out‐of‐field rejection of the more intense radiation from lower altitudes. High‐quality spectra were obtained with clearly identifiable features of CO2, O3, NO, OH, H2O, NO2, HNO3, and O2, as well as Rayleigh scattering. Spectra and tangent height emission profiles of selected species are presented and compared with theoretical emission models including those of Degges and Smith (Limb Model) and LOWTRAN 4. The salient findings are as follows: At a height of 80 km, CO2 daytime emission from fluorescence around 4.3 µm was almost 2 orders of magnitude greater than the nighttime emission. At 15 µm the CO2 radiance profiles showed little day‐night differences but exhibited an unexpected radiance plateau between 95 and 110 km. The ozone peak radiance at 9.6 µm (ν3) showed order of magnitude day‐night differences above 70 km tangent height showing a decrease in concentration of O3 during daytime due to photodissociation. The observed radiance in the 9‐ to 12‐µm wavelength region exhibited evidence of chemiluminescent emission from hot bands of O3. NO (Δυ = 1) peak radiance at 5.3 µm, due to O atom excitation, is a broad maximum at 120 km tangent height. The nighttime OH fundamental (Δυ = 1) and overtone (Δυ = 2) emissions showed extensive radiation from higher vibrational levels. The daytime 2.7‐µm fluorescent radiation was composed of emission from both H2O and CO2. Emission from NO2 at 6.15 µm (ν3) was observed at night only but was clearly identifiable amid the H2O (ν2) spectrum. Measured radiation in the 6.3‐µm vibrational band of water vapor at 60 and 70 km agrees with the Air Force Geophysics Laboratory non‐local thermodynamic equilibrium Limb Model using mixing ratios of 5 and 1.5 parts per million by volume, respectively. The radiance from O2 (a¹Δg) at 1.58 µm was observable from tangent heights of 30 to 80 km in the daytime only and shows a critical dependence upon the solar elevation angle. As expected, Rayleigh scattering was the dominant daytime source of radiation between 1 and 3 µm in the limb atmosphere for tangent heights of up to 40 km.

Earthlimb spectra of thermospheric NO fundamental band emissions, obtained in the CIRRIS 1A Space Shuttle experiment, have been analyzed using nonlinear least‐squares spectral fitting. Absolute NO(υ≥1,J) column densities have been determined in the 100 to 260‐km tangent height region and inverted to yield altitude‐dependent number densities for both a rotationally thermalized and a highly rotationally excited population component. Emissions from high‐J levels are predicted to dominate the Δυ=2 overtone bands during the daytime. The rotationally excited population is found to decrease more at night than the rotationally thermalized component. In addition, radiance from the CO υ=1→0 fundamental band is observed in the NO R‐branch band head region, with greater relative importance at night. The derived CO rotational temperatures are significantly greater than modeled local kinetic temperatures. These results provide important inputs to models of NO(υ,J) formation mechanisms, and of the chemistry, radiative processes, and energy budget of the thermosphere.

In this paper we present and discuss the cryogenic infrared radiance instrumentation for shuttle (CIRRIS) 15-•m CO2 and 5.3-•m NO data with respect to limb emission variability and within the context of latitudinal, diurnal, and geomagnetic variations during two days of observations onboard shuttle flight STS 39, April 29-30, 1991. About 50 limb emission profiles were examined for the two emissions. Enhancements were observed at high latitudes relative to midlatitudes and low latitudes at 140 km altitude for the 15-•m CO2 emission (factor of 2-5). The high-latitude enhancement in the 5.3-•m NO emission was larger (factor of 11-14). The high-latitude nighttime data were collected in the auroral zone during a class III aurora. Diurnal variations are examined at midlatitudes. A significant enhancement in the 15-•m emission was observed between 0500 and 0700 LT at 140 and 160 km. This effect was modeled by the SHARC atmospheric generator (SAG) which uses the mass spectrometer incoherent scatter (MSIS) model. Species concentrations from the thermosphere-ionospheremesosphere electrodynamics general circulation model (TIME-GCM) and SAG models were input to the SHARC radiance code to simulate the CIRRIS limb emission data.The TIME-GCM predicted the 15-btm CIRRIS radiances generally well for 100 km < z < 120 km but for higher altitudes the data was consistently a factor of 2 higher. For the 5.3-•m simulation the TIME-GCM predicted the data well at low latitudes and midlatitudes, but some significant discrepancies were found at higher latitudes. The altitude of the peak radiance of the 5.3-•m NO emission was found to vary between 110 to 135 km with little systematic global pattern. During high-latitude auroral events the peak of the 5.3-•m emission was consistently observed at higher altitudes than the peak of the 3914• N2 + first negative emission, in agreement with previous observations.