Intercomparison of Umkehr and differential absorption lidar stratospheric ozone measurements

A comparison of stratospheric ozone measurements using the Umkehr and differential absorption lidar (DIAL) techniques is presented. The ozone observations were made in Toronto, Canada (43.8 degrees N, 79.5 degrees W), using a Brewer ozone spectrophotometer and a DIAL co-owned by York University, the Institute for Space and Terrestrial Science, and the Atmospheric Environment Service. DIAL and Umkehr comparisons were made between January 1, 1991, and November 30, 1993. Our measurements show that under conditions of low aerosol loading, the Umkehr and DIAL ozone measurements overlap within their respective confidence intervals. After the Mount Pinatubo eruption the presence of aerosol affects both measurement techniques. The Umkehr retrievals are 20-40% lower than corresponding DIAL data at altitudes of 28 km and above. Below 28 km the DIAL data are similar to 35% lower than the Umkehr measurements. We apply aerosol corrections to the Umkehr data and observe overlap between DIAL and Umkehr measurements for altitudes greater than 28 km to within their respective error intervals throughout the entire period of observation.