Long-term variation of solar extreme ultraviolet fluxes

Abstract

The aeronomical importance of the 27-day variation of the incident solar EUV fluxes observed from the Oso 1 satellite over two successive solar rotations during spring 1962 has been discussed recently by Bourdeau et al. [1964] in this journal. Existing observational knowledge of variations over longer periods of time is even less satisfactory than that concerning these 27-day variations, since no continuous EUV monitoring experiments were ever made before the launch of Oso 1. Inferences of long-term variations of absolute intensities in the solar EUV spectrum based on a few short-lived rocket experiments must be treated with caution. In this letter we discuss the significance of certain long-term variations which are apparently implied by measurements variously covering the EUV range from 1300 A to 250 A and 310 A to 55 A, accomplished in rocket experiments with EUV monochromators by our group of the Air Force Cambridge Research Laboratories over the past five years. The essential results of these measurements obtained since the first successful monochromator flight of 1959 have been reported previously (except for results from the flight of December 12, 1963, which are presented here). References and data on EUV fluxes up to August 1960 were presented by Hinteregger [1961] and later work was discussed recently by Hinteregger et al. [1965].