Detecting Recovery in Vertically-resolved Ozone Records

Current estimates for the recovery rates of the ozone layer are very small: at mid-latitudes, recovery is expected to be only a few Dobson Units per decade over the next 50 years. Detecting this gradual recovery in the total column ozone record could take 15 to 35 years, even under the best of circumstances. Variations in the seasonal and altitudinal distributions of ozone suggest that evidence of recovery may be easier to detect during the local springtime, or at a single vertical layer in the atmosphere. This work investigates the length of time necessary to detect expected ozone recovery in geographically, seaonally, and vertically resolved records. The studies are based on our understanding of the magnitude of the trends expected for different seasons and locations, as well as on the variability and autocorrelation at those locations. Both factors--the size of the trend and the noise characteristics--are likely to influence where it will be easiest to detect future recovery. Estimates of past ozone variability are derived primarily from TOMS and SBUV-SBUV/2 observations, with intercomparisons to Dobson Umkehr, SAGE II and ozonesonde data. Chemical and coupled chemical-climate models, including the GSFC 2-D model and the GISS abbreviated 3-D model, provide estimates of expected recovery rates. Results include estimates of most optimal locations in terms of latitude, longitude and altitude for detecting future ozone recovery. The results also indicate at which times of year recovery can be expected to be resolved earliest. These findings can be useful for prioritizing future monitoring efforts to detect the expected recovery as early as possible. Estimates of recovery times produced now, early in the recovery phase, will be useful in explaining the complexity of the situation to all interested parties and may help ensure that future monitoring continues with the high levels of quality assurance necessary to detect recovery.