Looking back at the early years of Pc 1 pulsation research

Abstract

Geomagnetic pulsations—the groundbased signals of magnetospheric hydromagnetic waves—have been studied for well over 100 years. Some of the first observations were reported in 1861 by B. Stewart, who studied the recordings of the great magnetic storm of 1859. In Helsinki in the 1840s, J. J. Nervander observed magnetic “undulations” of constant period of about 30 s in his declination variometer.At the turn of the century, more sensitive magnetic instruments and faster registration systems were developed and the basis was laid for the systematic classification of long period pulsations, which are now called Pc 3‐Pc 5 and Pi 2 pulsations.