Relation between the secular variation of the Earth's magnetism and solar activity

Abstract

1. In a previous paper entitled “Solar Radiation and Terrestrial Magnetism,” the possibility was pointed out that irregularities in the annual changes of the Earth's magnetic elements, the so‐called secular variation, might be associated with such manifestations of solar activity as are revealed to us by changes in the solar constant of radiation. As the result of a preliminary investigation, the following conclusion was reached in that paper:If the quiet‐day magnetic effect were to persist throughout the year, it would cause a secular variation fully 10 times that generally observed. However, the quiet days are in the minority, being exceeded 3 times and more by unquiet days, on which the magnetic effect is of an opposite or compensating kind to that of the quiet day. Since these acyclic effects appear to be associated with solar changes and since the latter are not periodic, but more or less sporadic, there is an outstanding effect at the end of the year which causes an irregularity in the regularly‐progressing secular change. Accordingly, there should be found some correspondence between annual changes of the solar constant and annual magnetic changes. This is found to be the case. Since the solar‐constant changes occur only approximately in accordance with sun‐spot activity, and since the magnetic changes are found to conform closely to those in the solar constant, an explanation is found as to why the irregularities in the magnetic secular change do not always synchronize with changes in solar activity as measured by the sun‐spot numbers, nor correspond in magnitude to them.