First results of zonally averaged ClO concentrations as measured by MAS on ATLAS-1

The Millimeter wave Atmospheric Sounder (MAS) uses the limb sounding principle to detect atmospheric emission lines in the frequency range from 60 GHz to 205 GHz. MAS was flown for the first time during the ATLAS-1 mission in March 1992. The flight altitude of 300 km and an inclination of the orbit of 57° allowed to take measurements of ozone, water-vapor and chlorine monoxide (ClO) from 70°S to 70°N during day and night. The authors report on first results from measurements of the pressure broadened ClO-transitions around 204.352 GHz. As ClO exhibits a strong diurnal variability, vanishing during the night at most altitudes, the authors subtracted night spectra from day spectra in order to remove systematic errors and baseline ripple. Retrieval of ClO abundances has been performed in two ways. The difference spectra have been inverted by using the optimal estimation technique and information from apriori abundance profiles. This resulted in five independent layers of the retrieved ClO volume mixing profile, zonally averaged for latitudinal bands of 15°. On the other hand the total integrated spectral intensity has been determined for approx. 80 MHz around the center of the line. The spectral intensity is proportional to the column density along the path. This spectral intensity has been determined for 3 km thick layers in an onion peeling approach for an ideal pencil beam