Validation of stratospheric nitric acid profiles observed by Improved Limb Atmospheric Spectrometer (ILAS)–II

[1] The Improved Limb Atmospheric Spectrometer-II (ILAS-II) was launched aboard the Advanced Earth Observing Satellite-II (ADEOS-II) in December 2002. Stratospheric vertical profiles of nitric acid (HNO3) concentration observed by ILAS-II (version 1.4) are validated using coincident HNO3 measurements by balloon-borne instruments (MIPAS-B2 and MkIV) in March and April 2003. Further validation is performed by making climatological comparisons of lower stratospheric HNO3-ozone (O3) correlations obtained by ILAS-II and ILAS (the predecessor of ILAS-II) for specific potential vorticity-based equivalent latitudes and seasons where and when ILAS data showed very compact correlations in 1997. The reduced scatter of ILAS-II HNO3 values around the reference HNO3, which is derived from ILAS-II O3 using the ILAS HNO3-O3 correlation, shows that the precision of the ILAS-II HNO3 data is better than 13–14%, 5%, and 1% at 15, 20, and 25 km, respectively. Combining all of the comparisons made in the present study, the accuracy of the ILAS-II HNO3 profiles at 15–25 km is estimated to be better than −13%/+26%.

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