Short Periodicities in Latitudinal Variation of Sunspots

Abstract

The latitudinal variation of sunspots appearing during the period from 1874 to 2009 has been studied in terms of centerof-latitude (COL). The butterfly diagram has been used to study the evolution of the magnetic field and the dynamics at the bottom of the solar convection zone. Short-term periodicities have been of particular interest, in that they are somehow related to the structure and dynamics of the solar interior. We thus have focused our investigation on shortterm periodicities. We first calculated COL by averaging the latitude of sunspots with the weight function in area. Then, we analyzed the time series of COL using the wavelet transform technique. We found that a periodicity of ~5 years is the most dominant feature in the time series of COL, with the exception of the ~11 year solar cycle itself. This periodicity can be easily understood by considering small humps between the minima in the area-weighted butterfly diagram. However, we find that periodicities of ~1.3 (0.064), ~1.5 (0.056), or ~1.8 (0.046) years (1 month), which have been previously suggested as evidence of links between the changing structure of the sunspot zone and the tachocline rotation rate oscillations, are insignificant and inconsistent. We therefore conclude that the only existing short-term periodicity is of ~5 years, and that periodicities of ~1.3, ~1.5, or ~1.8 years are likely to be artifacts due to random noise of small sunspots.

Does Correction Factor Vary with Solar Cycle?

“…This is why the international scientific community has continuously renewed its interest in the sunspot number. Many scientific investigations, including cycle analysis and forecast, solar North-South asymmetry analysis, coherence analysis of the solar magnetic field, mid-term studies of solar activity, are based on the Solar Influences Data Analysis Center (SIDC) sunspot data (Pulkkinen et al 1999, Lockwood 2003, Solanki et al 2004, Wang 2004, Chang 2007, Usoskin 2008, Petrovay 2010, Ternullo 2010, Kim & Chang 2011.…”

Relative Sunspot Number Observed from 2002 to 2011 at ButterStar Observatory

“…As the study on the Sun-Earth system has become active, the variability of the Sun at various time scales is attracting more attentions (Pulkkinen et al 1999, Chang 2007, Petrovay 2010, Ternullo 2010, Kim & Chang 2011. Around a maximum of sunspot number, coronal mass ejections and powerful explosions on the solar surface, flares, occur more frequently.…”

Latitudinal Distribution of Sunspot and North-South Asymmetry Revisited

“…Since sunspots are formed as soon as the magnetic tube emerges from the solar surface, they can be considered tracers of emerged magnetic flux tubes. At the center of a sunspot, the magnetic field line is almost vertically aligned, with a field strength of about 2,500-3,500 G. Long-term observations of sunspots indicate that solar activity as a time series shows various periodicities, such as ~11 years (Schwabe 1843;Maunder 1904), ~80-90 years (Gleissberg 1971), ~1.3 years (Howe et al 2000;Krivova & Solanki 2002;Obridko & Shelting 2007;Kim & Chang 2011;Cho et al 2014), ~154 days (Rieger et al 1984), ~51, 78, 104, and 129 days (Bai & Sturrock 1991, 1993. In addition to variable sunspot records in time, the latitudinal position of sunspots with time provides invaluable information about the physical processes that generate the solar magnetic flux and induce its evolution.…”