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 (HNO 3) concentration observed by ILAS-II (version 1.4) are validated using coincident HNO 3 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 HNO 3 -ozone (O 3) 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 HNO 3 values around the reference HNO 3, which is derived from ILAS-II O 3 using the ILAS HNO 3 -O 3 correlation, shows that the precision of the ILAS-II HNO 3 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 HNO 3 profiles at 15-25 km is estimated to be better than -13%/+26%. Copyright 2006 by the American Geophysical Union.