Abstract
The status of the stratospheric ozone layer is assessed by a panel of experts every 4 years. Reports prepared by this panel include a section with common questions and answers (Q&A) about ozone depletion and related matters. Since 2002, this Q&A supplement has featured a plot comparing historical and current ultraviolet (UV) Index data from Palmer Station, Antarctica (64° S), with measurements at San Diego, California (32° N), and Barrow, Alaska (79° N). The assumptions in generating these plots are discussed and an updated version is presented. The revised plot uses additional data up to the year 2020 and the methods used to create it are better defined and substantiated compared to those used for the legacy plot. Differences between the old and new UV Index values are small (typically < 5%). Both versions illustrate that the ozone hole has led to a large increase in the UV Index at Palmer Station. Between mid-September and mid-November, the maximum UV Index at this site has more than doubled compared to the pre-ozone-hole era (i.e., prior to 1980). When Palmer Station was below the ozone hole in December 1998, an “extreme” UV Index of 14 was observed, exceeding the highest UV Index of 12 ever measured at San Diego despite the city’s subtropical latitude. Increases in the UV Index at Barrow and San Diego remain below 40% and 3%, respectively.Graphical abstract
Highlights
Background and introductionThe Montreal Protocol on Substances that Deplete the Ozone Layer [1] includes a provision to regularly convene panels of experts for assessing the effectiveness of this important international treaty
The updated datasets are very similar to data used for the questions and answers (Q&A) plot published in the last assessment report [6], but several differences can be discerned:
The updated plot is similar to the legacy plot but is based on longer time series, uses an updated dataset for Palmer, a slightly modified cosine error correction for San Diego, employs an improved method for reconstructing UVIs at Palmer for the pre-ozonehole period, and includes UVI reconstructions for San Diego and Barrow
Summary
Background and introductionThe Montreal Protocol on Substances that Deplete the Ozone Layer [1] includes a provision to regularly convene panels of experts for assessing the effectiveness of this important international treaty. The Q&A section of the 2002 assessment report [3] included for the first time a plot comparing modeled UV data for Palmer Station (“Palmer” hereafter) for a period prior to the formation of the Antarctic ozone hole (when no direct UV radiation measurements are available) with UV data measured between 1991 and 2001 when the ozone hole was well established. These data were contrasted with UV measurements from San Diego and Barrow (recently renamed to Utqiaġvik), Alaska (71° N), to provide a comparison with UV levels at low and high northern latitudes, respectively. The same plot was used for the assessment reports of 2014 and 2018 [5, 6]
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