Coronal Holes and the Solar Wind

Abstract

Around the turn of the century Professor Kristian Birkeland at the University of Kristiania (Oslo) carried out laboratory studies of the emission of charged particles from the Sun and their interaction with comets and magnetized planets. He found that cathode rays emitted by a magnetized sphere are bent toward the equator along trajectories similar to the structures observed in the solar corona during the 1901 eclipse. He also concluded that comet tails are formed by charged particles from the Sun interacting with dust and gas around the comet.Birkeland carried out extensive observing programs of the aurora, geomagnetic storms, and the zodiacal light. During a 9 months campaign from mid 1902 he observed recurrent geomagnetic storms from stations in Northern Norway, at Novaja Semlja, Iceland, and Spitsbergen, and correlated the occurence and periodicity of magnetic storms with solar activity. He found that the period of recurrent geomagnetic storms was generally larger than the period of “near equator” solar phenomena. He also found that “Very often large maxima of storminess are not accompanied by any sun-spots at all”. (Birkeland 1913, p. 524).