Alignment of Cirrus Clouds along the Magnetic Meridian

Abstract

CIRRUS clouds appear very often in a regular array of parallel bands. Alexander von Humboldt1 discovered in the course of his meteorological observations in South America and Siberia that these arrays follow frequently the line of the geomagnetic meridian of the locality; he invented the term “bandes polaires” for this phenomenon. Even very casual observations confirm the truth of his statement. He suspected some connexion between the appearance of these ‘polar bands’ and that of the aurora borealis. In the light of present-day knowledge of the composition of cirrus clouds, it is possible to put forward an explanation of this alignment. Since the constituent ice particles are known to form around dust particles of partly meteoric origin, they will align along the lines of force of the geomagnetic field in those cases in which the dust core consists of a magnetic material. It follows incidentally that the concentration of magnetic meteoric dust in the upper atmosphere should increase from the equator towards the poles, a hypothesis which is confirmed by Sobermann's2 recent work on the composition of noctilucent clouds above northern Sweden.