Intercomparisons between various atmospheric ozone datasets

Abstract

Ozonesondes provide direct measurements of ozone concentrations as a function of height in the atmosphere (OVP) and, therefore, also provide estimates of TOC. But these measurements are only made at a few geographical locations and often also somewhat infrequently. One important reason for studying atmospheric ozone in great detail is to identify long-term trends in ozone concentration and, in particular, to study the rate of recovery of the ozone layer in response to the implementation of the Montreal Protocol. Dobson spectrophotometers, and other ground-based instruments, have been used for many years and provide quite long-term datasets. The question of intercomparison of data from the various early laboratories is very important and has been discussed by Staehelin et al. (2009). These laboratories between them provided data for more than four decades before the beginning of anthropogenic ozone depletion; they included Arosa (Switzerland), Oxford (United Kingdom), Lerwick (United Kingdom), Tromso (Norway), Svalbard (Norway), and Vigna di Valle (Italy). However, Dobson spectrophotometers and other groundbased instruments only provide data for rather few geographical locations (see Figure 1.20). On the other hand satellite-flown instruments provide frequent data over enormous areas, approaching total global coverage, but they do not provide direct measurements of ozone concentrations; algorithms have had to be developed to determine TOC and OVP from the spectral data recorded by these instruments. Ground-based measurements constitute a key component of the Global Ozone Network, both on their own account and by providing ground truth for satellitebased instruments. However, the uneven geographical distribution of the existing ground-based network gives rise to a spatial sampling error, when attempts are made to determine the global distribution of ozone content. The benefit of ground-based instruments is that it is easy to maintain them in good condition, while the benefit of satellite-based instruments is that they provide better spatiotemporal coverage and resolution.