Does the magnetosphere behave differently on weekends?

Thomas Ulich, Jyrki Manninen, and Arto Karinen

Sodankylä Geophysical Observatory, FIN-99600 Sodankylä, Finland


In the 1970s indices of magnetic activity have been studied to reveal their long-term behaviour. Special attention was paid on their spectral composition. One of the results was that magnetic data from after the 1940s show enhanced geomagnetic activity on weekends. This effect was not observed before the 1940s. The reason for the so-called weekend effect was suggested to be the dramatic increase of consumption of electrical power due to human activity, which is larger during the working week than during weekends. Electrical power lines radiate into space and affect the magnetosphere. This is observed as so-called Power Line Harmonic Radiation (PLHR) in recordings of VLF waves. Also other effects of human activity, e.g. radio broadcasts, have been observed in VLF data.

In the present paper we study the 86 years of geomagnetic Ak index of Sodankylä, Finland, as well as its planetary counterpart Ap. We do not observe the weekend effect in those data. Additionally we study the digital data of the SGO pulsation magnetometers, which is available since 1995 continously, in order to reveal a possible weekday effect. Magnetic pulsations, esp. Pc1 pulsations, have been observed during magnetically quiet times after magnetic storms.