When the hole in the stratospheric ozone layer in Antarctica was discovered in 1985, the Montreal Protocol was signed to limit the emissions of chlorofluorocarbons (CFCs), gaseous components responsible for the ozone layer destruction. However, since the CFCs have a life span of several decades in the atmosphere, the ozone layer will be recovering very progressively. The observation of the stratospheric ozone by satellite on a global scale is crucial to make sure the measures taken are efficient.
GOMOS (Global Ozone Monitoring by Occultation of Stars) is an instrument developed by the European Space Agency supported by CNES and on board the European bus ENVISAT. It is an ultraviolet-visible spectrometer which observes a star when occulted by the atmosphere.
The ratio between the measured spectrum through the atmosphere and the spectrum of reference outside the atmosphere corresponds to the atmospheric transmission. It reveals absorption bands of atmospheric components, in particular ozone and oxides of nitrogen (NO2 and NO3). It is thus possible to establish a scheme of the tropopause's ozone (15 km) to the low thermosphere's (100 km). The stellar occultation technique offers a huge benefit not requiring a radiometric calibration, since the concentration of chemical species is deduced from a ratio of the spectrum independently from the absolute light emission received by the detector.
In partnership with investigators of the Finnish Meteorological Institute (FMI) and Belgian Institute for Space Aeronomy, the investigators of LATMOS-IPSL (CNRS/UPMC/UVSQ) are processing the data to extract the climatology of ozone and oxides of nitrogen on a global scale to study the reasons of the natural variability and due to human activity. Those results are aimed to determine if the stratospheric ozone layer does recover.
Many scientific results were obtained. They relate to:
- polar mesospheric clouds which form in Summer;
- relation between ozone, oxide of nitrogen and winds on the Equator (quasi-biennial equatorial oscillation);
- global climatology of ozone and oxides of NO3;
- secondary maximum of ozone at 90 km high;
- effects of solar particle rains on ozone and oxides of nitrogen in the polar region in Winter;
- turbulences and gravity waves in the stratosphere and link with the deep equatorial convection.