Different Phases Of Solar And Magnetic Activity Cycles

969 WordsAug 18, 20154 Pages
CHAPTER 2 Cosmic-Ray Modulation during Different Phases of Solar and Magnetic Activity Cycles INTRODUCTION Cosmic-rays are modulated as they traverse into the heliosphere. Measurements have shown that cosmic-ray intensity varies on different time scales. On a longer time scale, the cosmic-ray intensity variations in anti-phase with solar activity having ≈ 11-year cyclicity is well known and studied extensively (e.g., see Venkatesan and Badruddin, 1990; Storini et al., 1995; Usoskin et al., 1998; Mavromichalaki et al., 1998; Kane, 2003; Sabbah and Rybansky, 2006; Ma et al., 2009; Chaudhary et al., 2011; Kudela, 2012). In addition, the ≈ 22-year modulation cycle in cosmic-ray flux due to solar magnetic field polarity reversals is observed and modeled (e.g., Jokipii and Thomas, 1981; Potgieter and Moraal, 1985; Webber and Lockwood, 1988; Potgieter, 1995; Cliver and Ling, 2001; Laurenza et al., 2012). However, in order to understand these phenomena, it is important to understand how cosmic-ray transport and propagation vary with the solar activity and solar magnetic polarity (Heber, 2013). Although sunspots have been used as a convenient index of solar activity, anti-correlated with cosmic-ray intensity, it has been recognized that they are not intrinsically related to the problem of solar modulation of cosmic-rays. However, the diffusion coefficient changes during ≈ 11-year sunspot cycle, being smaller during periods of high solar activity than
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