Contribution à l'étude des relations entre les activités solaire et géomagnétique

Abstract

The article states the necessary conditions under which geomagnetic storms and disturbances arise, as revealed by observations of the Sun. The new criteria do not conflict with those previously developed, based on other phenomena. On the strength of these new ideas a method for forecasting geomagnetic activity has been elaborated, enabling a sudden commencement to be predicted with great accuracy. It makes possible the forecasting of geomagnetic storms in each period of the solar cycle, and to say in advance whether the onset of a given storm will be sudden or gradual. As examples for the purpose of explaining their origin, use has been made of the suddencommencement geomagnetic storms of llth February 1958, 20th September 1959, 29th October 1963, and 22nd November 1963. Except for the first, all these storms had been predicted on the basis of observations of the Sun by means of the spectrohelioscope. Furthermore, an explanation is given of the origin of the gradual-onset geomagnetic storm of 6th and 7th October 1960, which had likewise been predicted. On the same principles explanations are given of the geomagnetic quiet period of 19th–25th June 1965, which recurred six times (16th–17th July, 13th August, 8th–9th September, 6th–7th October, 1st–3rd November and 28th–29th November 1965) and of the one that occurred twice—on 31st December 1965 and 1st January 1966 and on 27th–28th January 1966.