Temporal Evolutions and Quasiperiodic Variations Present in the Sunspot Number and Group Sunspot Area Data Measured at Kodaikanal Observatory for Solar Cycles 14–24

Abstract

The Kodaikanal Observatory has made synoptic observations of the Sun in white light since 1904, and these images are sketched on the Stonyhurst grids called Sun charts. These continuous hand-drawn data sets are used for long-term studies of the Sun. This article investigates temporal and periodic variations of the monthly hemispheric sunspot number and sunspot group area for 1905–2016, covering solar cycles 14–24. We find that the temporal variations of the sunspot number and group area are different in each hemisphere and peak at different times of the solar cycle in the opposite hemisphere. For both data sets, Cycle 19 shows maximum amplitude. For the sunspot number time series, Cycle 24 was the weakest, and Cycle 15 for the group area. The existence of double peaks and violation of the “odd–even rule” was found in both data sets. We have studied the periodic and quasiperiodic variations in both time series using the wavelet technique. We noticed that, along with the fundamental mode of the ∼11 yr cycle and polarity reversal period of 22 yr, the sunspot activity data also exhibited several midterm periodicities in the opposite hemispheres, in particular the Rieger-group, and quasi-biennial periodicities. The temporal evolution of these detected quasi-periodicities also differs in the northern and southern hemispheres. We analyzed the data set statistically to understand the bulk properties and coupling between the opposite hemispheres. The study indicates that the two hemispheric data sets differ, but some dependency could be present.

Temporal and Periodic Analysis of Penumbra-Umbra Ratio for the Last Four Solar Cycles

“…The best known mid-term oscillations (MTOs) are the so-called quasi-biennial oscillations, QBO (see, for example, the comprehensive review by Bazilevskaya et al, 2014, and references therein). Another mid-term periodicity that was reported is sixyear oscillations (Prabhakaran Nayar et al, 2002;Ravindra et al, 2022). These variations are observed even in the full magnetic field of the Sun in "as a star" observations (Rivin and Obridko, 1992).…”

“…The wavelet analysis is a useful tool for examining the presence of localized oscillations, both in time and frequency domains. For this time series, we have considered ω 0 (non-dimensional frequency) as 12 for mid-term frequency (low periodic zone) and 6 for the low-frequency range (long periods) (Torrence and Compo, 1998;Ravindra, Chowdhury, and Javaraiah, 2021;Ravindra et al, 2022;Chowdhury et al, 2022, etc.,). The cone-of-influence (COI), where the wavelet power reduces by a factor e −2 due to edge effect, is plotted with a bold dashed line.…”

“…Later on, these type of periods with varying length between 130-190 days were detected in different solar and heliospheric activity indices including asymmetry time series as well as in the galactic cosmic ray data sets (e.g. Bai and Cliver, 1990;Bai and Sturrock, 1993;Carbonell and Ballester, 1992;Oliver, Ballester, and Baudin, 1998;Chowdhury, Khan, and Ray, 2009;Chowdhury et al, 2016Chowdhury et al, , 2022Knaack, Stenflo, and Berdyugina, 2005;Ravindra, Chowdhury, and Javaraiah, 2021;Ravindra et al, 2022;Kotzé, 2021;Korsós et al, 2023, etc.,) during different past solar cycles. These investigations suggest that Rieger types of periods are not only a feature of flare activity, but also connected with regions of compact magnetic field structures.…”

A new result on the long lived sunspot magnetic flux and their association with CME speed

“…The white-light photographs of the Sun have been captured on photographic plates at the KSO since 1902 (Pucha, Hiremath, and Gurumath, 2016;Ravindra et al, 2022;Priyadarshi et al, 2023). A 15 cm lens mounted on the front of the equatorial telescope projects the picture of the Sun onto the screen.…”

Helioseismic Investigation of Quasi-biennial Oscillation Source Regions

“…Studies based on solar observations show that the amplitude of the QBOs varies with the activity cycle, with the highest amplitudes during solar maxima that become weaker during the activity minima. During most solar cycle maxima, double peaks (with a Gnevyshev Gap) are more prevalent in activity indices, due to the asymmetry between the northern and southern hemispheres (Norton & Gallagher 2010;Ravindra et al 2022), where one hemisphere achieves the maximum amplitude earlier than the other hemisphere. It is also suggested that the solar cycle may evolve independently in the two hemispheres (e.g., Veronig et al 2021), which introduces asymmetry in both hemispheres.…”