Research Seminar by Paul Eriksen: "There is a new brewer in town"

Date: 30.04.2015

Time: 11.00 - 12.00

Place: Nordlys, DMI

Contact: Cathrine Fox Maule


A new instrument similar to the one shown in the photo below (Kangerlussuaq) secures continued observations of the Ozone Layer in Copenhagen.

It is now 75 years since DMI made the first observations of the ozone layer in Denmark. In the nick of time before Denmark was occupied by German troops an instrument to measure the thickness of the ozone layer came by ship to Aarhus in February 1940. It was an instrument built by Professor Dobson in Oxford and was part of his project to measure the ozone layer at several locations in Europe and to study how changes in the ozone layer could be used to make weather forecasts. Measurements were made by Professor Werner at the Institute for Physics, University of Aarhus, because the DMI did not have room for the instrument nor sufficiently trained personnel to operate the instrument. This so-called Dobson instrument was later exchanged with a newer instrument in 1963 purchased by the DMI but still operated in Aarhus until 1988. In 1992 a new Brewer Ozone Spectrophotometer, the successor of the Dobson instrument, and Brewer instrument #082, was purchased by the DMI following the fuzz created by the decline in the ozone layer caused by CFC’s. The subsequent forecast was an increase in harmful UV radiation. An added value of the Brewer instrument was that it could also measure global spectral UV radiation (thus UV-index). This was used to start the first UV-index-service in the world in May 1992 together with the Danish Cancer Society and the Photobiology Department at Rigshospitalet. This instrument is now 25 years old and shows its age: difficult to get spare parts, often troublesome when moved for calibration and not really good enough around mid-winter at this latitude. A new instrument has been wanted for several years to ensure continued observations of the ozone layer and the UV-index and finally we succeeded: instrument #228 came to DMI in late October 2014. Just in time to be able to compare it against the “old” instrument that is unable to measure accurately between 1st of November and 1st of February because the sun is too low. I will briefly touch on the history of ozone measurements in Denmark and then show how ozone is measured with the Dobson and Brewer instruments, how accurate they are, and what we do to maintain an accuracy of about 1% among the Brewer instruments in the World.