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

Abstract

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%.