Recent Improvements in Middle Atmosphere Remote Sounding Techniques: the Crista-Spas Experiment

In November 1994 and in August 1997 the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment was flown aboard the ASTRO-SPAS (ASTROnomical Shuttle PAllet Satellite) freeflying platform launched by the Space Shuttle. The main aim of CRISTA is to detect small dynamical features in trace constituents of the middle atmosphere. The instrument is therefore equipped with three telescopes which collect the infrared radiation from three different air volumes at the earth limb. High recording speed and high radiometric sensitivity is obtained from cryogenic cooling of the optics and of the detectors. Radiation is analysed by grating spectrometers in the wavelength range from 4 μm to 71 μm and in the altitude regime from the upper troposphere to the middle thermosphere. The spatial resolution as well as the latitudinal coverage of the measurement net is further improved by making use of the satellite pointing and manoevering capabilities. The improvements in the performance of middle atmosphere limb soundings obtained from the combination of the CRISTA instrument concept and the ASTRO-SPAS pointing capabilities are illustrated by a few examples from the two missions. These results include narrow streamers of ozone rich air observed in the subtropics at 30 km, sharp transport barriers in O 3 , and small scale temperature fluctuations over the Andes which were identified as gravity waves. A special thermospheric observation mode provided the first global measurement of the fine structure emission of atomic oxygen at 63 μm.