Long-term variations in north-south asymmetry of solar activity

Abstract

We present a new set of data on relative sunspot number (total, northern hemisphere, and southern hemisphere), taken for the 37-yr period 1947 to 1983; this constitutes a particularly coherent and consistent set of data, taken by the same observer (Hisako Koyama) using the same observing instrument. These data are combined with earlier data (White and Trotter, 1977) on the variation of sunspot areas for both solar hemispheres from 1874 to 1971. The combined data, covering 110 years and 10 solar cycles, are examined for periodicity in solar activity north-south asymmetry. We show that, in general, northern hemisphere activity, displayed as either An/(An + As) or Rn/(Rn + Rs), peaks about two years after sunspot minimum. This peak is greater during even cycles, pointing to a 22-yr periodicity in north-south asymmetry in solar activity, suggesting that the asymmetry is related to the 22-yr solar magnetic cycle. We demonstrate that the largest and most protracted period of northern-hemisphere activity excess in the last 110 years has occurred from 1959 to 1970; we show that there is a strong correlation between northern activity excess and a cosmic-ray density gradient perpendicular to the ecliptic plane, pointing southward, which is evident in cosmic-ray diurnal variation data from the Embudo underground cosmic-ray telescope.

Latitudinal Distribution of Sunspots Revisited

“…This is why various solar activity indices, such as, sunspot number, sunspot area, flare index, are studied. Asymmetries between the northern and southern hemispheres have been previously found in various solar indices (Waldmeier 1971, Roy 1977, White & Trotter 1977, Ichimoto et al 1985, Swinson et al 1986, Özgüç & Ücer 1987, Verma 1987, Tritakis et al 1988, Vizoso & Ballester 1989, Antonucci et al 1990, Mouradian & Soru-Escaut 1991, Schlamminger 1991, Yi 1992, Carbonell et al 1993, Verma 1993, Oliver & Ballester 1994, Javaraiah & Gokhale 1997, Li et al 1998, Ataç & Özgüç 1996, Temmer et al 2001, Krivova & Solanki 2002, Vernova et al 2002, Berdyugina & Usoskin 2003, Knaack et al 2004, Ballester et al 2005, Gigolashvili et al 2005a, b, Javaraiah & Ulrich 2006, Zaatri et al 2006, Chang 2007a, b, 2008, 2009. This is the second motivation for the present study.…”

“…One may also wish to check its validity of some research on the latitudinal migration of solar activity. For example, some researchers have reported that latitudinal migration of sunspots asynchronously occur in the northern and southern hemispheres (Waldmeier 1971, Swinson et al 1986, Zolotova & Ponyavin 2006, Donner & Thiel 2007, Zolotova et al 2009, Li et al 2009a, b, 2010. They have attempted to explain the solar North-South asymmetry with such a phase difference between paired wings of the butterfly diagram instead of appreciating the real asymmetry in two hemispheres.…”

Latitudinal Distribution of Sunspots and Duration of Solar Cycles

“…By replotting the butterfly diagram by weighting the sunspot with its area, one may observe intriguing features of solar magnetic activities more clearly (see, e.g., Chang 2011). For example, latitudinal migration of center-of-latitude (COL) occur asynchronously in the northern and southern hemispheres as reported earlier (Swinson et al 1986;Zolotova & Ponyavin 2006Li et al 2010). Furthermore, COL is not monotonically decreasing as commonly assumed.…”

“…To further investigate the solar North-South asymmetry, many solar activity indices have been thoroughly examined (Waldmeier 1971;Roy 1977;Swinson et al 1986;Yi 1992;Carbonell et al 1993;Oliver & Ballester 1994;Meunier et al 1997;Temmer et al 2002Temmer et al , 2006Hathaway et al 2003;Gigolashvili et al 2005;Zaatri et al 2006;Zolotova & Ponyavin 2006Donner & Thiel 2007;Chang 2008Chang , 2009Javaraiah 2008;Li 2010;Li et al 2010). Since it was established, the North-South asymmetry is also considered as one of the most interesting fea-326 Chang Figure 1.…”

Ms. Hisako Koyama: From Amateur Astronomer to Long‐Term Solar Observer

“…Swinson et al (1986) used the "particularly long and coherent data set" from the Koyama record combined with other related data to examine the north-south asymmetry in solar activity over many solar cycles. Swinson et al (1991) further investigated the significance of such asymmetries as they relate to cosmic ray density gradients.…”