CIRRIS 1A GLOBAL OBSERVATIONS OF 15-MU-M CO2 AND 5.3-MU-M NO LIMB RADIANCE IN THE LOWER THERMOSPHERE DURING MODERATE TO ACTIVE GEOMAGNETIC-ACTIVITY

In this paper we present and discuss the cryogenic infrared radiance i nstrumentation for shuttle (CIRRIS) 15-mu m CO2 and 5.3-mu m NO data w ith respect to limb emission variability and within the context of lat itudinal, diurnal, and geomagnetic variations during two days of obser vations onboard shuttle flight STS 39, April 29-30, 1991. About 50 lim b emission profiles were examined for the two emissions. Enhancements were observed at high latitudes relative to midlatitudes and low latit udes at 140 km altitude for the 15-mu m CO2 emission (factor of 2-5). The high-latitude enhancement in the 5.3-mu m NO emission was larger ( factor of 11-14). The high-latitude nighttime data were collected in t he auroral zone during a class III aurora. Diurnal variations are exam ined at midlatitudes, A significant enhancement in the 15-mu m emissio n 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 m ass spectrometer incoherent scatter (MSIS) model. Species concentratio ns from the thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) and SAG models were input to the SHARC r adiance code to simulate the CIRRIS limb emission data. The TIME-GCM p redicted the 15-mu m 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-mu m simulation the TIME-GCM predicted the data well at low latitudes and midlatitudes, but some significant discrepan cies were found at higher latitudes. The altitude of the peak radiance of the 5.3-mu m NO emission was found to vary between 110 to 135 km w ith little systematic global pattern, During high-latitude auroral eve nts the peak of the 5.3-mu m emission was consistently observed at hig her altitudes than the peak of the 3914 Angstrom N-2(+) first negative emission, in agreement with previous observations.