COMPARISON OF CORRELATIVE DATA WITH HNO3 VERSION-7 FROM THE CLAES INSTRUMENT DEPLOYED ON THE NASA UPPER-ATMOSPHERE RESEARCH SATELLITE

The cryogenic limb array etalon spectrometer (CLAES) aboard UARS made near-global measurements of HNO3 and 388 days from January 9, 1992, to April 25, 1993, have been processed to data version 7 (V7). Results f rom UARS instruments, including CLAES, the improved stratospheric and mesospheric sounder, and the microwave limb sounder, provide the first near-global documentation of the evolution of denitrification in the Antarctic 1992 winter and spring vortex. We provide a description of t he CLAES HNO3 V7 quality that includes comparisons with correlative me asurements to assess overall quality, accuracy, and precision. Correla tive profiles of volume mixing ratio (vmr) included those obtained by the space shuttle deployed ATMOS in two missions, March-April 1992 and April 1993, data from a variety of balloon-borne instruments at midla titude (11 profiles), and in high-latitude northern winter (six profil es), and LIMS data. In general, the CLAES V7 HNO3 maximum values of vm r were of the order of 6-15% less than correlative for CLAES values le ss than or equal to 8 parts per billion by volume (ppbv). However, whe n CLAES peak vmr values were 10 to 13 ppbv, then CLAES values exceeded correlative by 0-7%. The comparisons were within the combined instrum ental error estimates, or observed measurement variability, for the la rge majority of comparisons. As discussed, the retrieval of future ver sions will utilize updated spectral parameters and will also correct f or a small uncompensated drift in radiometric calibration that occurre d in the latter part of the mission. This is expected to improve the c omparisons in the less than or equal to 8 ppbv range, perhaps at the e xpense of those in the greater than or equal to 8 ppbv range. The data obtained January 9 to April 15, 1992, in comparison with data obtaine d January 9 to April 15, 1993, reveal strikingly evident 1-year period deseasonalized trends on a global basis. These trends agree quantitat ively with available correlative data suitable fur trend analysis. The se include ATMOS in the southern midlatitudes and published longterm t ime series of HNO3 column obtained at 45 degrees S and 20 degrees N. T hese trends reveal a large decrease in the southern hemisphere and sma ll increases in the northern hemisphere, such that the global average is toward a decrease. The global average decrease we attribute to the diminishing influence of heterogeneous conversion of N2O5 to HNO3 as t he Pinatubo aerosol settles out during this time period, and the HNO3 recovers toward pre-Pinatubo conditions. We establish plausibility tha t the small increases in the north are due to hemispherically asymmetr ic QBO-like effects that are strong in the northern hemisphere and wea k in the southern hemisphere and are phased to produce an increase in HNO3 over the 1-year time period of just the right magnitude to more t han offset decrease due to settling out of the Pinatubo aerosol. Based on this study, our range of confidence in the CLAES HNO3 V7 product i s from 70 to 3 mbar, in comparison with correlative data, and the prec ision on this range is of the order of 0.3-1.0 ppbv. This precision wa s derived from data repeatability and agrees within a factor of 2 or b etter with estimates based on instrument characterization and with err or estimates embedded within the V7 data.