Abstract
Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs) measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between "substorm" and "quiet" atmospheric currents decreases. The amplitude of this "substorm" variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.Key words: Ionosphere (electric fields and currents) · Magnetospheric physics (storms and substorms) · Meteorology and atmospheric dynamics (atmospheric electricity)
Highlights
The global electric circuit, in which atmospheric currentsow from the ground to the ionosphere in low-latitude regions, and spread all over the globe and return to the ground through the fair weather regions, has been widely studied over the last 30 years
Our goal is to study the eect of the ionospheric substorm generator on the air±earth vertical currents (AECs) using measurements carried out at ground level in northern Sweden with this type of antenna
We have investigated by means of superposed epoch analysis the inuence of geomagnetic substorms on fair weather air-earth currents measured near the ground
Summary
The global electric circuit, in which atmospheric currentsow from the ground to the ionosphere in low-latitude regions, and spread all over the globe and return to the ground through the fair weather regions, has been widely studied over the last 30 years. The three main generators, or energy sources, of this circuit are believed to be thunderstorms, the ionospheric dynamo (tides) and the solar wind/magnetosphere dynamo (Roble and Tzur, 1986). Thunderstorms, which occur mostly at equatorial and subequatorial latitudes maintain the potential dierence of 150±600 kV (Muhleisen, 1977) between the ground and the ionosphere. Tides in the ionosphere lead to the appearance of a horizontal potential dierence of 5±15 kV between high and low latitudes at ionospheric heights (Richmond, 1986). Solar wind-magnetosphere coupling results in an additional ionospheric potential drop of 40±100 kV across the polar caps
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