(Source: DLR, KNMI, ACRI)
The ozone layer is of vital importance for life on Earth because it strongly absorbs the harmful ultra-violet (UV) radiation from the Sun. The discovery of a rapid decline of ozone over Antarctica each spring - the ozone hole - in the mid 1980s came as an unexpected and unpleasant surprise. Since the discovery of the ozone hole in 1984 a steady negative trend has been observed in the ozone abundance over the South Pole. This trend is related to the presence of man-made chlorofluorocarbons (CFCs).
Implementation of the international Montreal protocol has resulted in a large reduction of emissions of CFCs and to a recently observed decrease of CFC concentrations in the atmosphere. As a consequence the Antarctic ozone hole is expected to recover this century. However, future predictions of this expected recovery remain uncertain. The recovery will depend on complex climate-chemistry interactions associated to the greenhouse effect. It will further depend on the development of emissions of ozone-depleting substances.
The discovery of the ozone hole, and the subsequent international measures taken as a result of the Montreal protocol, demand a world-wide and long-term monitoring of the ozone layer, both from the ground and from space.
Especially the successful NASA Total Ozone Mapping Spectrometer (TOMS) instruments and the Solar Backscatter UltraViolet (SBUV) instruments have played a crucial role in monitoring the global ozone distribution and the changes in the Antarctic and Arctic ozone layer in particular. These measurements are available since 1979 and document the deepening of the ozone hole in the 1980s and the year-to-year variations of ozone until the present day.
The European contribution to this long-term ozone column monitoring has started with the Global Ozone Monitoring Instrument (GOME) on ERS-2, launched in 1995. This data set is continued with GOMOS, MIPAS and SCIAMACHY on Envisat, launched in 2002. The TOMS ozone record will be continued with the Dutch-Finnish Ozone Monitoring Instrument (OMI) on the NASA EOS-Aura satellite, launched in 2004. The instruments on Envisat will provide an important contribution to the perceived high accuracy of the ozone total column (on the few percent level) measured in the UV-visible (SCIAMACHY), and the profiling capability in limb (MIPAS and SCIAMACHY) and by observing the occultaion of stars (GOMOS) which contributes to their success. An important requirement for the ozone data sets is the long-term stability which should be of the order of 1% in order to document ozone trends and the possible recovery of the ozone layer.
The PROMOTE ozone monitoring service is a response to the demand for consistent global total and 3D ozone analyses and ozone records, and aims to provide easy access to these data sets. The PROMOTE service provides both the satellite observation data sets and value-added assimilated ozone fields based on multiple sensor ozone data. These fields are obtained by combining ozone observations with chemical-transport models driven by meteorological analyses.
The assimilation of atmospheric ozone is illustrated in figure 1. Ozone columns from SCIAMACHY nadir measurements, which become available a few hours after the measurement, serve as input for the assimilation analysis of the stratospheric ozone layer. For SCIAMACHY it takes six days to reach global coverage. With the assimilation a complete description is obtained of the world-wide ozone distribution and it's evolution with time.
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Figure 1. Left: a collection of 24 hours of SCIAMACHY ozone column data for 23 February 2005. Right: North-Pole view of the assimilated ozone field at 12 GMT, based on SCIAMACHY data as shown in panel a. The figures show abnormally low ozone values over the Northern Atlantic, related to ozone depletion and the presence of polar stratospheric clouds, in combination with a special atmospheric circulation in this month. Ozone columns are given in Dobson units. |
Ronald van der A, Thilo Erbertseder, Henk Eskes. Last modified: June 2005