The aim is to obtain consistent measurements from a network of ground-based spectrometers by means of collection and analysis of data, and intercomparison with data obtained by other SESAME projects. The research especially aims at a climatology of constituents observed by ground-based UV-visible instrumentation. The constituents to be observed are O3, NO2 and, if possible, OCIO, BrO, stratospheric aerosols and polar stratospheric clouds (PSCs). The data base for the UV-visible region reaches back to 1987/88. Therefore interannual variations will be discernible.
Stratospheric measurements will be carried out throughout 1994 and 1995 by ground-based UV-visible instruments. The unpredictable movements of the arctic vortex require instruments at various locations. The vortex position will be followed, to determine the location of stations relative to the vortex. Measurements will be made at high and at lower latitudes. An important objective is to monitor the effect of air masses transported from high to lower latitudes.
The daytime (twilight) column densities of stratospheric trace gases are measured by ground-based observations os sunlight scattered from the zenith sky. There will be automated instruments (SAOZ) and non-commercial instruments operated in the spectral range from 300 to 700 nm.
The absorptions are due to the column of molecules absorbing along the slant path between the light source and the observer. Before the weak atmospheric absorption bands are detectable, the much stronger solar Fraunhofer structure must be removed. This is accomplished by dividing by a rererence spectrum containing no other molecular absorptions from the Earth's atmosphere.
The network of UV-visible spectrometers includes the following stations:
Station Location Responsible
Ny Ålesund 79°N, 12E NILU
Thule 77°N, 69°W DMI
Scoresbysund 70°N, 22°3 CNRS
Søndre Strømfjord 67°N, 51°W NOAA (DMI)
Sodankylä 67°N, 27°E FMI, CNR
Zhigansk 67°N, 124°E CNRS
Fairbanks 65°N, 149°W UA
Bremen 53°N, 9°E UB
Jungfraujoch 47°N, 8°E BIRA, MPI
Haute Provence 44°N, 6°E CNRS
Huelva 37°N, 6°E INTA
Canary Island 28°N, 17°E INTA
Réunion Island 24°S, 55°E UR, CNRS
Dumont d'Urville 67°S, 140°E CNRS
Funding SchemeCSC - Cost-sharing contracts