A Study of the Hemispheric Asymmetry of Sunspot Area During Solar Cycles 23 and 24

Abstract

Solar activity indices vary over the Sun's disk, and various activity parameters are not considered to be symmetric between the northern and southern hemispheres of the Sun. The north-south asymmetry of different solar indices provides an important clue to understanding subphotospheric dynamics and solar dynamo action, especially with regard to nonlinear dynamo models. In the present work, we study the statistical significance of the north-south asymmetry of sunspot areas for the complete solar cycle 23 (1996-2008) and rising branch of cycle 24 (first 45 months). The preferred hemisphere in each year of cycles 23 and 24 has been identified by calculating the probability of hemispheric distribution of sunspot areas. The statistically significant intermediate-term periodicities of the north-south asymmetry of sunspot area data have also been investigated using Lomb-Scargle and wavelet techniques. A number of short-and mid-term periods including the best-known Rieger one (150-160 days) are detected in cycle 23 and near Rieger-type periods during cycle 24, and most of them are found to be time variable. We present our results and discuss their possible explanations with the help of theoretical models and observations.

Three-Year Global Survey of Coronal Null Points from Potential-Field-Source-Surface (PFSS) Modeling and Solar Dynamics Observatory (SDO) Observations

“…(Chowdhury, Choudhary, and Gosain, 2013). There was a noticeable dominance of the southern hemisphere at the end of Cycle 23 and then the northern one at the beginning of Cycle 24.…”

“…All of the observed and predicted CNPs were first broken into two different groups as shown in Figure 7. The top graph consists of 103 observed and 229 predicted CNPs between 16 June 2010 to 25 May 2012, when the solar activity was dominated by the northern hemisphere; also, the bottom graph has 80 observed and 160 predicted CNPs between 26 May 2012 to 15 August 2013, when the southern hemisphere became dominant according to sunspot areas (Chowdhury, Choudhary, and Gosain, 2013). The dashed line indicates the normalized latitudinal distribution of observed CNP counts, while the solid line shows the same for the predicted CNPs.…”

“…Figure 7. The latitudinal distribution of CNPs when the northern (top) and southern (bottom) hemispheres were dominant according to sunspot areas (Chowdhury, Choudhary, and Gosain, 2013). All of the observed and predicted CNPs are indicated by the dashed and solid line, respectively.…”

Sunspot latitudes during the Maunder Minimum: A machine-readable catalogue from previous studies

“…Moreover, the asymmetry of the data was analyzed from the point of view of the probability of having such an asymmetric distribution by random fluctuation. This can be done using the cumulative binomial probability (Press et al 1989;Chowdhury and Dwivedi, 2011) 1 that, in this context, provides the probability of having a number of sunspots equal or greater that k in the southern hemisphere (n and p being, respectively, the total number of sunspots and the random probability -p = 0.5 in our case-of having a sunspot in the southern hemisphere). Above equation can be expressed in terms of the incomplete beta function (Abramowitz and Stegun, 1972) , 1 Table 1.…”

Latitudinal Distribution of Sunspots and Duration of Solar Cycles

“…tures in relating to solar activity (Knaack et al 2005;Javaraiah 2007Javaraiah , 2015Chang 2011Chang , 2012Pesnell 2012;Chowdhury et al 2013;Pandey et al 2015).…”