VALIDATION OF CLAES CLONO2 MEASUREMENTS

The cryogenic limb array etalon spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite has made extensive measurements of therm al infrared radiation from the Earth's limb from which vertical concen tration profiles of several stratospheric gases and multiwavelength ae rosol absorption coefficients have been retrieved for the period from January 9, 1992, to May 5, 1993. This work examines stratospheric ClON O2 concentrations from the current calibration and retrieval software which are designated version 7 data. These data provide the first near -global view of this stratospheric species. This work evaluates data q uality through (1) an analysis of estimated uncertainties and biases i n the remote sensing process, (2) comparison with calculations using a two-dimensional chemical model, (3) comparison with correlative data, and (4) an examination of various known limitations. The precision of CLAES ClONO2 volume mixing ratio retrievals are within 15% in the ran ge (10 < P < 50 mbar). The upper limit on estimated systematic error i s 28% in the range (10 < P < 100 mbar) based on studies of error sourc es in midlatitude retrievals. The global distribution of ClONO2 comput ed with the Lawrence Livermore National Laboratory two-dimensional str atospheric chemistry model and the CLAES measurements agree qualitativ ely. However, above the profile peak the calculated concentration freq uently exceeds the measurement. CLAES and ATMOS measurements show rela tively good midlatitude agreement, suggesting that the major sourer of discrepancy is in the model. A possible explanation in terms of a mis sing reaction ClO + OH --> HCl + O-2 is suggested. Also, the ClONO2 di urnal cycle constructed from more than 30 days of CLAES data agrees we ll with the model. The CLAES ClONO2 data differ from correlative data acquired on flights of the shuttle-based ATMOS and balloon-borne instr uments by less than 25% on the average in the 10 < P < 50 mbar range. At altitudes above 10 mbar the CLAES measurement is biased low with re spect to correlative measurements. This discrepancy at high altitudes is consistent with the analysis showing a large increase of systematic errors above 10 mbar. Heavy tropical volcanic aerosol from the Mount Pinatubo eruption in June 1991 apparently interfered with ClONO2 retri evals in the period before July 1992, causing anomalous peaks in the 2 0 < P < 30 mbar region accompanied by very small concentrations below the peak (P > 30 mbar). A similar effect associated with thick polar s tratospheric clouds is identified. Overall, this validation study indi cates that the majority of these data are of good quality and should b e very useful in quantitative and qualitative chemical studies of the stratosphere.