Long Term Variations in Chromospheric Features from Ca-K Images at Kodaikanal

Priyal, Muthu; Singh, Jagdev; Ravindra, B.; Priya, T. G.; Amareswari, K.

doi:10.1007/s11207-013-0315-7

Cited by 46 publications

(112 citation statements)

References 22 publications

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“…The digitized full disc century-long (1907 to mid-2007) 4096×4096 Ca II K solar images (»0.8036 arcsec pixel −1 ) from KSO (Figures 1(a)-(b)) used in this study were recorded through a telescope with a 30 cm objective, with an f-ratio of f/ 21 (Priyal et al 2014b) and a spatial resolution of about 2 arcsec. We employed a few calibration steps before the feature detection was performed: flat fielding, disc detection and centering, north-south rotation correction, intensity inversion, and limb darkening correction.…”

Section: Methodsmentioning

confidence: 99%

“…We employed a few calibration steps before the feature detection was performed: flat fielding, disc detection and centering, north-south rotation correction, intensity inversion, and limb darkening correction. The Hough circle transform (Sonka et al 2014) was applied on the edge detected raw images to efficiently identify the disc center and radius, in contrast to the manual method described in earlier work by Priyal et al (2014b). The radius varied by some number of pixels systematically over time due to a change in the SunEarth distance during each revolution.…”

Section: Methodsmentioning

confidence: 99%

“…This should ideally be a radially symmetric function, but due to atmospheric and instrumental effects it loses the symmetry. In contrast to the radially symmetric polynomial method of limb darkening estimation for KSO data as presented in Priyal et al (2014b), the current study captured the variation by applying a 40×40 2D median filter (Zharkova et al 2005;Bertello et al 2010) on the resized 512×512 disc centered images. This essentially performs blurring to represent large scale intensity variation (Figures 2(b)- (c)).…”

Section: Limb Darkening Correctionmentioning

confidence: 99%

“…Thus Ca II K line emission provides a good proxy for line-of-sight (LOS) magnetic field fluxes, particularly for the historical period for which regular direct magnetic field measurements are not available (Skumanich et al 1975;Schrijver et al 1989). The Kodaikanal Solar Observatory (KSO) has archived full disc Ca II K spectroheliograms for more than a century (1906 to mid-2007), using photographic plates as recorded through a telescope with a 30 cm objective, with an f-ratio of f/21 (Priyal et al 2014b). The effective spatial resolution was about 2 arcsec for the majority of the documentation time.…”

Section: Introductionmentioning

confidence: 99%

“…Note that this comparison was made based on earlier low resolution scanned images (as obtained from KSO) and the need for higher resolution digitization was pointed out by Ermolli et al (2009). The first results from the new digitization process were reported in Priyal et al (2014b) using KSO data on Ca II K for the period . We have recalibrated the data for the full 100 years and are presenting the first results from the new time series.…”

Section: Introductionmentioning

confidence: 99%

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A BUTTERFLY DIAGRAM AND CARRINGTON MAPS FOR CENTURY-LONG Ca ii K SPECTROHELIOGRAMS FROM THE KODAIKANAL OBSERVATORY

Chatterjee

Banerjee

Ravindra

2016

ApJ

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The century-long Ca II K spectroheliograms from the Kodaikanal Solar Observatory (KSO) are calibrated, processed, and analyzed to follow the evolution of the bright on-disc structures called plages, possible representatives of magnetic activity on the Sun. This is the longest data set studied in Ca II K to date, covering about 9.5 cycles of 11 yr periods. Plages are segmented with area 1 arcmin 2 using global thresholds for individual full disc images and subsequent application of a morphological closing operation. The plage index is calculated and is seen to have a close positive correlation with the fractional disc area covered by plages. The newly generated plage area cycle (from KSO) was compared with the same from the Mount Wilson Observatory (correlation 95.6%) for the overlapping years, i.e., 1915-2000. This study illustrates the time-latitude distribution of plage centroids by rendering a butterfly diagram (as observed for sunspots). The 3D visualization of the diagram shows one-to-one mapping between plage location, time, and area. This work further delineates the positional correlation between magnetic patches and plage regions through the comparison of synoptic maps derived from both KSO Ca II K images and space-based full disc line-of-sight magnetograms. Regular synoptic magnetograms from ground-based observatories are available only after 1970s. Thus the long term Ca II K data from KSO can be used as a proxy for estimating magnetic activity locations and their strengths at earlier times.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Limb Darkening Correctionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A BUTTERFLY DIAGRAM AND CARRINGTON MAPS FOR CENTURY-LONG Ca ii K SPECTROHELIOGRAMS FROM THE KODAIKANAL OBSERVATORY

Chatterjee

Banerjee

Ravindra

2016

ApJ

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Solar Cycle Indices from the Photosphere to the Corona: Measurements and Underlying Physics

Ermolli

Shibasaki

Tlatov

et al. 2015

Space Sciences Series of ISSI

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A variety of indices have been proposed in order to represent the many different observables modulated by the solar cycle. Most of these indices are highly correlated with each other owing to their intrinsic link with the solar magnetism and the dominant eleven year cycle, but their variations may differ in fine details, as well as on short-and long-term trends. In this paper we present an overview of the indices that are often employed to describe the many features of the solar cycle, moving from the ones referring to direct observations of the inner solar atmosphere, the photosphere and chromosphere, to those deriving from measurements of the transition region and solar corona. For each index, we summarize existing measurements and typical use, and for those that quantify physical observables, we describe the underlying physics.

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Mid-term quasi-periodicities in the CaII-K plage index of the Sun and their implications

Chowdhury

Gokhale²,

Singh

et al. 2016

Astrophys Space Sci

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Long Term Variations in Chromospheric Features from Ca-K Images at Kodaikanal

Cited by 46 publications

References 22 publications

A BUTTERFLY DIAGRAM AND CARRINGTON MAPS FOR CENTURY-LONG Ca ii K SPECTROHELIOGRAMS FROM THE KODAIKANAL OBSERVATORY

A BUTTERFLY DIAGRAM AND CARRINGTON MAPS FOR CENTURY-LONG Ca ii K SPECTROHELIOGRAMS FROM THE KODAIKANAL OBSERVATORY

Solar Cycle Indices from the Photosphere to the Corona: Measurements and Underlying Physics

Mid-term quasi-periodicities in the CaII-K plage index of the Sun and their implications

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