Cosmic-ray intensity versus solar soft X-ray background in cross-correlation analysis

The relationship between the galactic cosmic ray modulation (CR) and the no n-flare coronal level, as given by the solar soft X-ray background (XBG), i s investigated from 1 July 1968 to 30 June 1980 on a daily basis. The stati onarity problem of a multivariate time series, as well as the role of the s hort- and medium-term corona variability are faced. From them it is found t hat the CR/XBG relation is variable during the considered heliomagnetic sem icycle, while CR and XBG are highly anticorrelated on a long-time scale (12 -month averages). The CR/XBG relationship during the declining phase of sol ar activity shows a moderately strong anticorrelation, on short- and medium -term time scales (coefficient up to -0.77 for 27-day running averages), we nt towards insignificant values in the minimum phase and is only partially reconstructed during the rise of the following solar cycle. During the sola r activity maximum of cycle 20 the cosmic-ray modulation is only related to the short-term coronal fluctuations (no other time scales are significant, supporting the reliability of the so-called 'Gnevyshev gap' in solar param eters).