Total Column Ozone, Return years

Estimated MMM1S return dates (red triangles) of total column ozone from the SEN-C2-fCH4 simulations for different latitude bands. Credit: S.S. Dhomse et al., Supplement of Atmos. Chem. Phys., 18, 8409–8438, 2018

As mentioned in the previous section, the time series of total column ozone (zonally averaged) can be normalized using satellite observations of ozone data. Usually a year before the decline of ozone in the 1980s is used for the normalization. If the year 1980 is taken, then we use the measurements of the ozone column and move all the model time series up or down so that they pass through the point of measurement. Since ozone has been decreasing from that point and has slowly recovered and is rising again, we are able to check when in the future ozone will be at the same level as in 1980 again. Having done this we can plot the time of ozone returning to 1980 level for each model and for different seasons/months/latitude bands.