CIRRIS 1A global observations of 15‐µm CO2 and 5.3‐µm NO limb radiance in the lower thermosphere during moderate to active geomagnetic activity

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In this paper we present and discuss the cryogenic infrared radiance instrumentation for shuttle (CIRRIS) 15‐µm CO2 and 5.3‐µm 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‐µm CO2 emission (factor of 2–5). The high‐latitude enhancement in the 5.3‐µm 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‐µm 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‐ionosphere‐mesosphere 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‐µm 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‐µm 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‐µm 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‐µm emission was consistently observed at higher altitudes than the peak of the 3914Å N2+ first negative emission, in agreement with previous observations.