Trend analysis of aerosol‐corrected Umkehr ozone profile data through 1987

Abstract

Trend analysis of stratospheric Umkehr ozone profile data from 10 stations over the period 1977–1987 is considered. Two different correction methods to adjust the Umkehr data measurements for errors caused by volcanic aerosols, the theoretical model‐based corrections method of DeLuisi et al. (1989) and an empirical method based on use of a composite optical thickness series, are examined and compared. Linear trend models which also include the F10.7 solar flux term to account for solar cycle variations in the Umkehr data were estimated for the Umkehr data at each station using both aerosol error correction methods. The trend and solar flux effect estimates are generally similar for both methods. The results indicate a significant overall negative trend, exclusive of trend variations associated with solar flux variations, of the order of −0.5% per year in Umkehr layers 7–9 over the period 1977–1987, and a significant positive solar cycle association in all layers 4–9, with the maximum solar effect estimated to occur in layer 9. A comparison between the solar backscattered ultraviolet (SBUV) monthly average ozone profile data near the 10 Umkehr stations and the corresponding Umkehr data corrected for aerosol errors is performed to investigate possible drifts, and linear drifts are estimated for the differences between SBUV and corrected Umkehr data at each station. The results show a substantial overall negative linear drift in SBUV data relative to corrected Umkehr data in layers 7–9, with estimated values of the drift of the order of −1.0% per year for layers 8 and 9.