Variations in Ca-K line profiles and Ca-K line features as a function of latitude and solar cycle during the 20th century

Abstract

The analysis of the Ca-K line spectra as a function of latitude and integrated over the visible disk obtained during the period of 1989–2011 at the Kodaikanal Solar Tower Telescope shows that the FWHM of the K1 distribution at different latitudes varies by negligible amount at about 60° latitude whereas it varies significantly at other latitudes. Findings, especially the fewer variations in mid-latitude belts as compared to polar regions and complex variation in the shift in the activity around 60° latitude belt, will have important implications on the modeling of solar dynamos. Further, we have generated a uniform set of digitized Ca-K line images by selecting images considering the intensity distribution of the images corrected for the instrumental vignetting for the data obtained at Kodaikanal during the 20th century. Then, we have determined the percentage of plage and network areas by using the intensity and area threshold values.

Delving into the Historical Ca ii K Archive from the Kodaikanal Observatory: The Potential of the Most Recent Digitized Series

“…Our results for the plage areas from DS2 data show worse agreement with the series by Ermolli et al (2009b) and Tlatov, Pevtsov, and Singh (2009) from analysis of DS1 data than our results from DS1 data. However, we also notice a worse agreement with our results from DS2 data and those by Priyal et al (2017) and Singh et al (2018) from analysis of DS2 data than our results from DS1 data.…”

“…Table 2 lists the RMS difference and the Pearson coefficient between the various series when daily values are used. The best agreement is found between our results and those by Chatterjee, Banerjee, and Ravindra (2016) and Singh et al (2018), although when annual values are used then the agreement is better with the series by Ermolli et al (2009b) and Tlatov, Pevtsov, and Singh (2009). However, there are hints of a non-linearity between our plage areas and those by Tlatov, Pevtsov, and Singh (2009).…”

“…The number of common days is given within the brackets. The abbreviations CEA16, EEA09, PEA17, and SEA18 refer to the Chatterjee, Banerjee, and Ravindra (2016), Ermolli et al (2009b), Priyal et al (2017), and Singh et al (2018) The error bars denote the RMS error in the derived plage areas due to the disc ellipticity and the processing to photometrically calibrate the images (the latter is applicable only to the Kodaikanal data) as found by Chatzistergos et al (2019b). Bottom: Difference of plage areas derived from the 757 images common to DS2 and Rome/PSPT series plotted against the number of the image.…”

“…Figure 15 shows scatter plots between the plage areas derived by us from the DS2 data and the various published series obtained from Kodaikanal observations. In particular we consider the series by Kuriyan, Muralidharan, and Sampath (1983) derived from the physical photographs, the series by Ermolli et al (2009b) and Tlatov, Pevtsov, and Singh (2009) from the DS1 data, and the series by Chatterjee, Banerjee, and Ravindra (2016), Priyal et al (2017), and Singh et al (2018) from the DS2 data. Note that the series by Kuriyan, Muralidharan, and Sampath (1983) and Tlatov, Pevtsov, and Singh (2009) are only available as annual values and most likely include different selections of observations.…”

“…This information was not stored, but rather was used to crop and center the images. These cropped images were then used by Chatterjee, Banerjee, and Ravindra (2016), Priyal et al (2017), andSingh et al (2018) to derive their plage areas. Ermolli et al (2009b) and Tlatov, Pevtsov, and Singh (2009) defined the radius and center coordinates for DS1 independently.…”