Comparison of Stratospheric Aerosol and Gas Experiment (SAGE) II version 6.2 water vapor with balloon‐borne and space‐based instruments

A new version of the SAGE II data products was released in October 2003. The primary change to the algorithm dealt with improvements in the water vapor product such as eliminating the dry bias in the lower stratosphere and reducing the sensitivity to aerosol contamination. Results of an extensive comparison of SAGE II version 6.2 water vapor and various correlative measurement from balloon‐borne and space‐based instruments illustrate significant improvement over the previous version (version 6.1). In general, the agreement was within 10% or less over an altitude range of 15–40 km when compared with frost point hygrometer, HALOE, POAM III, and ILAS and 15–20% when compared to MkIV. Above 40 km, SAGE II water vapor profiles are often noisy and show an increasingly positive bias. On the basis of comparison with HALOE a basic screening criteria would consist of electing measurements where the aerosol extinction coefficient at 1020 nm exceeds 2 × 10 −4 km −1 and water vapor uncertainty exceeds 50%.