Annales Geophysicae, 20, 1137-1142, 2002.
1Dept of Physical Sciences, University of Oulu, Oulu, Finland
2Sodankylä Geophysical Observatory, Sodankylä, Finland
Global geomagnetic activity has been suggested to be enhanced during weekends above the weekly average after 1930. Before the 1930s weekends and weekdays were found to be equally active. This so-called "weekend effect" was suggested to be due to power line harmonic radiation (PLHR) in VLF range emitted by electric power lines. Since the consumption of electric power is different on weekends and weekdays leading to different PLHR intensities, this could possibly cause the "weekend effect" in global geomagnetic activity.
In the present paper we reanalyse the suggested "weekend effect" in global geomagnetic activity using the 69-year planetary geomagnetic Ap index and the 131-year antipodal aa index. We conclude that there is no statistically significant "weekend effect" during the interval covered by these geomagnetic activity indices. Although global geomagnetic activity is slightly enhanced on weekends from the 1930s to the 1980s, the more recent data show rather a relative decrease of global geomagnetic activity on weekends, contrary to the expected increase of the "weekend effect" due to increasing power consumption. Moreover, the weekly distribution is fairly similar in solar wind speed and global geomagnetic activity during the last 35 years, further supporting the view that the "weekend effect" is only statistical fluctuation.