Intercomparison of ILAS‐II version 1.4 aerosol extinction coefficient at 780 nm with SAGE II, SAGE III, and POAM III

Abstract

The Improved Limb Atmospheric Spectrometer (ILAS)‐II on board the Advanced Earth Observing Satellite (ADEOS)‐II observed stratospheric aerosol in visible/near‐infrared/infrared spectra over high latitudes in the Northern and Southern hemispheres, intermittently from January to March and continuously from April through October 2003. This study assesses the data quality of ILAS‐II version 1.4 (V1.4) aerosol extinction coefficient at 780 nm. In the Northern Hemisphere (NH), aerosol extinction coefficient (AEC) from ILAS‐II agreed with extinctions from SAGE II and SAGE III within ±10% and with extinction from POAM III within ±15% at heights below 20 km. From 20 to 26 km, ILAS‐II AEC was smaller than extinctions from the other three sensors; differences between ILAS‐II and SAGE II ranged from 10% at 20 km to 34% at 26 km in the NH. Over the Southern Hemisphere (SH), ILAS‐II AEC from 20 to 25 km in February was 12–66% below SAGE II extinction. The difference increased with increasing altitude. Comparisons between ILAS‐II and POAM III from January to May in the SH (“non‐PSC season”) yielded qualitatively similar results. From June to October (“PSC season”), ILAS‐II extinction was also smaller than POAM III extinction above 17 km; however, ILAS‐II extinction agreed with POAM III extinction to within ±15% from 12 to 17 km during the PSC season. The comparisons indicate that in both hemispheres the ILAS‐II V1.4 AEC is comparable to extinctions from other measurements below approximately 20 km and systematically low above approximately 20 km although the mean difference is as small as ∼2 × 10−5 km−1 during the non‐PSC season.