A long series of measurements of the surface potential gradient have been made since 1962 in Sweden in the Marsta Observatory (59◦56 N; 17◦35 W) located in rural area 10 km north of Uppsala. Nearest forest is located more than 1 km from the observatory, which provides undisturbed micro-meteorological conditions. There are no industrial establishments around the observatory. The closest sources of possible air pollution are the town of Uppsala. A modifed atmospheric electrical station of the Kasemir–Dolezalek construction is used. During long periods other electric and meteorological parameters are measured.
The Marsta Observatory is recommended as a basis station for long-term routine atmospheric electric measurements to gather data for the study of climate variation because of the large weight of global component in the variation of fair weather air-earth electricity.
The study shows that the effect of local air pollution appears essentially less than at other evaluated continental atmospheric electric stations. The diurnal variations at Marsta are well correlated with the Carnegie curve during winter and ill correlated during summer.
Our long-term measurements during the years 1962—2002 show no pronounced changes in the vertical potential gradiant. Other previous long-term measurements in Europe, however, show a long-term decrease in the vertical potential gradient.
The differences in the observations can be due to changes in the surroundings of the observation sites. Baloon measurements of the ionospheric potential from 50 years measurements at different places over the globe show no long-term trend. But according to the Wilson model the global integrator of the atmospheric electricity is the conducting ionosphere and the variations are caused by the variations in thunderstorm activity that depends on the continental area illuminated by the Sun. A publication during 2006 shows, however, that the lightning activity in Tropical Africa has a maximum during 1960s and follows by a decrease in activity during the following 30 years, which can support a decrease of the long-term change of the potential gradient at the surface layers. Global warming is becoming discussed during a long time and the anthropogenic activity on our planet is strongly discussed connected to this.
"Global electrical circuit", "atmospheric electricity", "atmospheric electrical fields"