Does the magnetosphere behave differently on weekends?

A Karinen,K Mursula,Th Ulich,J Manninen

doi:10.5194/angeo-20-1137-2002

Abstract

Abstract. 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 the 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 "week-end 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 geo-magnetic 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 in global geomagnetic activity on weekends, contrary to the expected increase in 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 a statistical fluctuation.Key words. Geomagnetism and paleomagnetism (time variations, diurnal to secular) – Magnetospheric physics (planetary magnetospheres; storms and substorms)

Highlights

IntroductionElectrical power lines radiate waves in the VLF (very low frequency, 300 Hz – 30 kHz) range at harmonics of their fundamental frequency, which is usually 50 or 60 Hz
Electrical power lines radiate waves in the VLF range at harmonics of their fundamental frequency, which is usually 50 or 60 Hz
Since global geomagnetic activity is known to have increased fairly systematically during the last 100 years, this might have led to the “weekend effect” when weekly averages are compared with the values of the subsequent weekends

Summary

Introduction

Electrical power lines radiate waves in the VLF (very low frequency, 300 Hz – 30 kHz) range at harmonics of their fundamental frequency, which is usually 50 or 60 Hz. Fraser-Smith (1979) reported that global geomagnetic activity had increased during weekends since the 1930s. He studied global geomagnetic activity by the 7-day superposed epoch analysis using the daily values of the Ap and aa indices in the 46.5-year (1 January 1932 – 6 June 1978) and 110-year (1 January 1868 – 31 December 1977) intervals, respectively. According to Fraser-Smith (1979), global geomagnetic activity is smaller on weekdays because the strong PLHR affects the magnetospheric processes so that natural disturbances are suppressed. 4, we present a detailed time profile for the “weekend effect” using the 131-year aa index.

Superposed epoch analysis of the Ap index

Spectral analysis of the Ap index

Long-term evolution of the “weekend effect”

Conclusions