Analysis of Trends in Total Stratospheric Ozone

Time series of total column ozone have exhibited unusual, unexpected behavior over the past few years. In 2016, total ozone was lower than expected based on some analyses that utilize the time evolution of equivalent effective stratosphere chlorine (EESC). Conversely, total column ozone exhibited a sharp rise in 2017. The existence of a new formulation (i.e., Engel et al., ACP, 2017) for the fractional release factors (FRFs) used to find EESC for mid-latitude lower stratospheric air parcels, the contribution of very short-lived chlorine and bromine compounds to EESC, as well as possible temporal variations in tropospheric column ozone compound the difficulty in establishing a quantitative relationship between the time evolution of EESC and stratospheric ozone. This presentation will consist of an analysis of the 40 year record of total column ozone measured from space (e.g., version 8.6 of the NASA SBUV Merged Ozone Data Set), along with:

- stratospheric chlorine loading from various satellite instruments as well as the long-term ground-based measurement from Jungfraujoch, Switzerland;

- various other quantities that affect the long-term evolution of stratospheric ozone (e.g., total solar irradiance, stratospheric optical depth, quasi-biennial oscillation of the direction of tropical stratospheric winds)

- estimates of tropospheric column ozone

to assess our understanding of trends in total stratospheric ozone. Preliminary results indicate better quantitative understanding is attained when using the new FRFs, which leads to a more gradual recovery of total stratospheric ozone than is found using the old FRFs.

Reference: Engel, A. et al., ACP, 18, 601-619, doi:10.5194/acp-18-601-2018, 2018.