Radioactivity soundings of the upper atmosphere in Finland 1962-2022

Abstract

Radioactivity soundings have been performed in Finland since the early 1960s to measure radiation and radioactivity levels in the atmosphere up to the altitude of almost 40 km. A sonde package based on a Geiger‐Müller (GM) tube is carried up to the stratosphere by a balloon filled with hydrogen or helium. En route the GM tube count rate values are sent to the ground station with a radio transmitter. These radioactivity soundings revealed the presence of abnormal radioactivity in the stratosphere over Finland due to Soviet atmospheric nuclear tests in 1962. Between 1964 and 1980 artificial radioactivity in the stratosphere originating from the Chinese nuclear tests were observed too. The radioactivity soundings have brought information on cosmic radiation even if the main motivation has been the surveillance of artificial radioactivity in the upper atmosphere. The effects of the solar cycle, geomagnetic latitude and solar proton events on the radiation environment of the upper atmosphere have been measured. The produced vertical ionization profiles may also be useful in studies concerning ion‐induced or ion‐mediated new particle formation events in the atmosphere.