Periodic and Quasi-Periodic Variations in the Ca K Index During the 20th Century Using Kodaikanal Data

Priyal, Muthu; Singh, Jagdev; Ravindra, B.; B, Chandar Shekar

doi:10.1007/s11207-019-1522-7

Cited by 15 publications

(26 citation statements)

References 30 publications

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“…For the period of time between 1923 and 2011, a total of 24,939 images are available to be used for the present investigation, out of which around 23,200 are of very good quality. Details of the telescope (Sivaraman et al 1993) and the digitization process of the images can be obtained, for example, in Ravindra et al (2013) or Priyal et al (2019).…”

Section: Methodsmentioning

confidence: 99%

Nearly Century-scale Variation of the Sun’s Radius

Hiremath

Rozelot

Sarp

et al. 2020

ApJ

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The Kodaikanal Archive Program (India) is now available to the scientific community in digital form as daily digitized solar white light pictures, from 1923 to 2011. We present here the solar radius data, obtained after a painstaking effort to remove all effects that contribute to the error in their measurements (limb darkening, distortion of the objective lens, refraction, other instrumental effects, etc.). These data were analyzed to reveal any significant periodic variations, after applying a multi-taper method with red noise approximation and the Morlet wavelet transform analysis. After removing obvious periodic variations (such as solar rotation and Earth annual rotation), we found a possible cycle variation at 11.4 yr, quasi biennial oscillations at 1.5 and 3.8 yr, and Rieger-type periodicity at ≈159, 91, and 63 days. Another ≈7.5 yr periodicity (as a mean) resulting from two other main periodicities detected at 6.3-7.8 yr can be identified as an atmospheric component. The detrending data show, over a mean radius of 959".7 ± 0".7, a residual of less than ≈(−)1 mas over the time period of analysis: if not spurious, this estimate indicates a faint decline, but probably confirms more the constancy of the solar diameter during the considered ranging time, within instrumental and methodological limits. The Kodaikanal long quality observations contribute to international efforts to bring past solar data measurements to the community to further explore issues, for instance, those of the luminosity/radius properties that could be used to pinpoint the "seat of the solar cycle."Unified Astronomy Thesaurus concepts: Solar radius (1488)

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Section: Methodsmentioning

confidence: 99%

Nearly Century-scale Variation of the Sun’s Radius

Hiremath

Rozelot

Sarp

et al. 2020

ApJ

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“…About two-third of the total images come under the category of "Good" time-series. Priyal et al (2019) determined the threshold value of intensity and area to determine the different features mentioned above. But the threshold values for the study of variations as a function of latitude are different from those for the whole image, since some part of plages and networks are likely to fall in two latitude belts.…”

Section: Data and Analysismentioning

confidence: 99%

“…Using these images we see pole-and equator-ward shift in the activity; thereby the meridional flows have been studied. The magnetic images of the Sun for the earlier times are not available but other types such as Ca-K, Hα are available since the beginning of 20th century (Oliver, Ballester, and Baudin, 1998;Gopalswamy, 2008;Sindhuja, Singh, and Ravindra, 2014;Priyal et al, 2019 and the references cited therein). The cyclic variations of these features are known as the solar cycle.…”

Section: Introductionmentioning

confidence: 99%

Variation of Chromospheric Features as a Function of Latitude and Time Using Ca-K Spectroheliograms for Solar Cycles 15 – 23: Implications for Meridional Flow

et al. 2021

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We have analyzed the Ca-K images obtained at Kodaikanal Observatory as a function of latitude and time for the period of 1913 -2004 covering Solar Cycles 15 to 23. We have classified the chromospheric activity into plage, Enhanced Network (EN), Active Network (AN), and Quiet Network (QN) areas to differentiate between large strong active and small weak active regions. The strong active regions represent toroidal and weak active regions poloidal component of the magnetic field. We find that plage areas mostly up to 50 • latitude belt vary with about 11-year solar cycle. We also find that a weak activity represented by EN, AN and QN varies with about 11-year with significant amplitude up to about 50 • latitude in both hemispheres. The amplitude of the variation is minimum around 50 • latitude and again increases by a small amount in the polar region. In addition, the plots of plages, EN, AN and QN as functions of time indicate the maximum of activity at different latitude occur at different epoch. To determine the phase difference for the different latitude belts, we have computed the cross-correlation coefficients of other latitude belts with the 35 • latitude belt. We find that the activity shifts from mid-latitude belts towards equatorial belts at high speed at the beginning of a solar cycle and at lower speed as the cycle progresses. The speed of the shift varies between ≈ 19 and 3 m s −1 considering all the data for the observed period. This speed can be linked with the speed of meridional flows, believed to occur between convection zone and the surface of the Sun.

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“…Worden et al (1998) showed that the intensity contrast of active regions is beyond the intensity contrast of quiet chromosphere. Priyal et al (2019) found that in the normalized intensity distribution of the image, intensity contrast greater than 1.30 represents plages and enhanced network (EN), intensity contrast between 1.20 to 1.30 represents active network (AN), and intensity contrast between 1.10 to 1.20 represents quiet network (QN). The remaining pixels, forming a large area of the sun, with intensity contrast lying between about 0.9 to 1.10 values, approximately follows the Gaussian distribution representing a quiet chromosphere.…”

mentioning

confidence: 99%

“…Still, the FWHM of the intensity distribution is likely to remain the same with minor variations, if any. But FWHM of the intensity distribution was found to be related to the contrast of the images and much larger for high contrast images than for images with very low contrast (Priyal et al 2019). Therefore, by making the FWHM of the intensity distribution the same for all the images, it is possible to make the contrast of the long-time series data the same.…”

mentioning

confidence: 99%

Determining the Variations of Ca-K index and Features using a Century Long Equal Contrast Images from Kodaikanal Observatory

Singh,

Priyal,

Ravindra

2020

Preprint

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In the earlier analysis of Ca-K spectroheliograms obtained at Kodaikanal Observatory, the "Good" images were used to investigate variations in the chromosphere. Still, the contrast of the images varied on a day-to-day basis. We developed a new methodology to generate images to form a uniform time series. We adjusted each image's contrast until the FWHM of the normalized intensity distribution attained a value between 0.10 and 0.11. This methodology of the "Equal Contrast technique" is expected to compensate for the change of emulsion, development, contrast of the images due to centering of Ca-K line on the exit slit and sky transparency. Besides, this procedure will correct variations in density-to-intensity conversion for different images. We find that the correlation between sunspot and Ca-K line data improves by a large amount.For example, correlation coefficient (CC) between monthly averaged sunspots and Ca-K plage areas for the equal contrast data improves to 0.9 compared to 0.75 for the "Good" data with unequal contrast. The CC for equal contrast images improves to ∼0.78 from ∼0.46 for the "Okay" data with unequal contrast. Even the CC between the plage area and the daily sunspot number is 0.85 for 100 years of data. This methodology also permits us to study the variations in Enhanced, Active, and Quiet networks with time

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Periodic and Quasi-Periodic Variations in the Ca K Index During the 20th Century Using Kodaikanal Data

Cited by 15 publications

References 30 publications

Nearly Century-scale Variation of the Sun’s Radius

Nearly Century-scale Variation of the Sun’s Radius

Variation of Chromospheric Features as a Function of Latitude and Time Using Ca-K Spectroheliograms for Solar Cycles 15 – 23: Implications for Meridional Flow

Determining the Variations of Ca-K index and Features using a Century Long Equal Contrast Images from Kodaikanal Observatory

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