Fair Weather Atmospheric Electricity

Atmospheric Research Programme - AEC

Many people (even scientists!) are unaware that the atmosphere carries a continuous electric current and, even during fair weather, there is a strong electrostatic electric field, up to 200 volts per meter, close to the ground. This electric current is thought to be due to the accumulated effect of thousands of thunderstorms, mostly in the tropical regions of the Earth. These storms feed a current from the ground up to the ionosphere, a highly conducting layer in the atmosphere which lies above about 70 km altitude. The current spreads out around the globe through this layer and returns to Earth through the atmosphere as the 'fair weather current' outside the thunderstorm areas.

Although the existence of the global electric circuit has been known for many decades, most recent research has concentrated on the 'generators', i.e. the thunderstorms. There are many gaps in our knowledge concerning, for example, the contribution of other generators such as the solar-wind and the upper atmosphere tides.

Site of long wire antenna at Esrange
(The small hut houses the sensor electronics and data logging computer and the antenna hangs on the wooden poles following the hillside to the right.)

We do not know either how changes in the electrical conductivity in the atmosphere affect the currents or voltages in the different parts of the circuit, nor how it interacts with aerosol layers in the atmosphere. Since changes in solar activity directly modify the latter two generators, and the atmospheric conductivity (through cosmic rays) there is a potential for solar-activity driven changes in the global electric circuit. Even anthropogenic pollution can be expected to lead to changes through increasing aerosol loading of the atmosphere, which reduces conductivity.

Research here aims to study these questions. Observations of the fair weather current have been made since 1998 using a long wire antenna (100 m long) situated near the top of a hill at Esrange. Short periods of trial measurements have been made in 2002 and 2003 at the Swedish Antarctic station, Wasa. Similar measurements are also made in Sodankylä in Finland. It is important to have measurements from several sites in order to separate local (meteorological) variations from true fair-weather global effects.

Locations of the measurement sites Esrange and Wasa

Site of long wire antenna at Wasa, Antarctica

Quick-look plots of the current collected by the antennas are available in our archive. Note that these are often highly disturbed by local meteorology and only representative of the fair weather current on really fair weather days!

Responsible scientists are Evgenia Belova and Sheila Kirkwood

Latest update: webmaster*irf.se, 2011-07-21.