Statistical properties of world-wide fluctuations in the magnetic field

Abstract

The common periods with which world-wide geomagnetic fluctuations occur in the period range of 6-150 min during disturbed conditions have been computed from spectrum analysis of horizontal force at several equatorial stations. The spectrums suggest a dominant period with peak power near 120 min and a 'half power' width of about 100 min. Shorter period secondary oscillations with periods around 25 and 37 min have also been noticed in the spectrums. The longer period oscillations appear to be caused by changes in the solar wind structure. The periods associated with relatively faster oscillations agree fairly well with the eigen-periods computed by several workers from their studies of the natural resonances of the geomagnetic tail.