CORONAL I NDEX OF SOLAR A CTIVITY: Y EARS 1939-1963 (1994)

A coronal index of solar activity (CI), based upon the total irradiance of the coronal 530.3 nm green line, has been constructed for the period 1939-1963 from observations at five stations worldwide. The monthly average CI exhibits a cyclic pattern with time, with succesive peaks monotonically increasing since solar cycle 18. Potential uses of the CI are discussed. The origin of solar activity is one of the basic problems of solar physics. In order to solve the problem we need to introduce a measure of solar activity - some index. One approach toward understanding solar activity involves studying the temporal relationship between different forms of activity; to do this, indices of the different types of solar activity would be useful. A second reason for developing a solar activity index is its potential value in studying the solar influence on the interplanetary and terrestrial environment. This direction of research was stressed last, because some proof exists of a connection between solar activity level and the total irradiance of the Sun, e.g. Pap et al. (1991). The basis for the establishment of different solar activity indices are observations of individual features of solar activity, e.g. sunspots, flares, prominences, radio flux, etc. Also the fluxes (emissions) from regions (lines) of the electromagnetic spectrum, from X-ray to radio flux, are introduced. Each of such indices has its own advantage or disadvantage. As examples, first, the longest data set, the Wolf sunspot number (It), is determined from visible wavelength observations of the solar surface. The disadvantage of this index is that we do not know the substance of the sunspots; therefore, we do not know how to derive the physical influences of the index. Second the disadvantage of indices derived from measurements of radio flux of the Sun is the anisotropy of irradiance and conditions of its propagation. A most natural index of solar activity- especially for solar-terrestrial study-would seem to be the flux of emissions which arises at some regions (lines) of the X or EUV part of the spectrum. However, these emissions do not pass through the Earth's atmosphere, and they may only be observed from satellites. At present, these observations may only be made over short time intervals. The hardest emission and the highest variation (amplitude) of flux is generally valid for these indices. Some X-ray emissions from the solar corona have variable fluxes that are caused by the same processes which are responsible for the increase of coronal emission line intensities. This was the basic idea for creating a coronal index of solar activity (CI). The index is derived from ground-based observations (around the solar limb) of the 530.3 nm coronal line. This green sdar corona is emitted by Fe XIV ions and is observed presently at only four coronal stations, according to international agreement. Interrupted data for the green corona have been available since 1939. CI represents the total irradiance of the green corona into one sterradian towards Earth. An exact definition of CI and the method of its calculation are described by Rybansk~ (1975), Itybansk2~ eta). (1993 and references therein). We note that CI data were published