Solar physics at Kodaikanal

Bappu, M. K. V.

doi:10.1007/bf00150312

Cited by 24 publications

(13 citation statements)

References 2 publications

(2 reference statements)

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“…Spectropolarimetric observations were carried out using a newly added dual beam polarimeter to the spectrograph at Kodaikanal solar telescope (Nagaraju et al (2007) and also see Bappu (1967) for details about the spectrograph and telescope setup). The wavelength region of the observations presented in this paper includes H α (λ6563) and Fe I (λ6569) lines.…”

Section: Instrument and Observationsmentioning

confidence: 99%

On the Weakening of the Chromospheric Magnetic Field in Active Regions

Nagaraju

Sankarasubramanian

Rangarajan

2008

ApJ

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Simultaneous measurement of line-of-sight (LOS) magnetic and velocity fields at the photosphere and chromosphere are presented. Fe I line at λ6569 and H α at λ6563 are used respectively for deriving the physical parameters at photospheric and chromospheric heights. The LOS magnetic field obtained through the centerof-gravity method show a linear relation between photospheric and chromospheric field for field strengths less than 700 G. But in strong field regions, the LOS magnetic field values derived from H α are much weaker than what one gets from the linear relationship and also from those expected from the extrapolation of the photospheric magnetic field. We discuss in detail the properties of magnetic field observed in H α from the point of view of observed velocity gradients. The bisector analysis of H α Stokes I profiles show larger velocity gradients in those places where strong photospheric magnetic fields are observed. These observations may support the view that the stronger fields diverge faster with height compared to weaker fields.

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Section: Instrument and Observationsmentioning

confidence: 99%

On the Weakening of the Chromospheric Magnetic Field in Active Regions

Nagaraju

Sankarasubramanian

Rangarajan

2008

ApJ

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“…The routine Ca K observations have been going on in Kodaiakanal since 1906 (Bappu 1967). The spectroheliograms which were obtained in photographic plates are presently being digitized and calibrated.…”

Section: Observationsmentioning

confidence: 99%

Network and plage indices from Kodaikanal Ca-K data

Raju¹,

Singh²

2014

Res. Astron. Astrophys.

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The Ca II K filtergrams from Kodaikanal Solar Observatory have been used to study the solar activity. The images are dominated by the chromospheric network and plages. Programs have been developed to obtain the network and plage indices from the daily images as functions of solar latitude and time. Preliminary results from the analysis are reported here. The network and plage indices were found to follow the sunspot cycle. A secondary peak is found during the declining activity period in both the indices. A comparison of network indices from the northern and the southern hemispheres shows that the former is more active than latter. However such an asymmetry is not clearly seen in the case of plage index.

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“…Normally, in the morning the Earth's atmospheric seeing is good at Kodaikanal. Clouds cover the sky in the afternoon, and in the evening it clears up again (Bappu 1967;Smith 1895). Most of the time the images are taken early in the morning before 10 hr (IST).…”

Section: Observational Datamentioning

confidence: 99%

Digitized archive of the Kodaikanal images: Representative results of solar cycle variation from sunspot area determination

Ravindra

Priya

Amareswari

et al. 2013

A&A

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Context. Sunspots have been observed since Galileo Galilei invented the telescope. Later, sunspot drawings have been upgraded to image storage using photographic plate in the second half of nineteenth century. These photographic images are valuable data resources for studying long-term changes in the solar magnetic field and its influence on the Earth's climate and weather. Aims. Digitized photographic plates cannot be used directly for the scientific analysis. It requires certain steps of calibration and processing before using them for extracting any useful information. The final data can be used to study solar cycle variations over several cycles. Methods. We digitized more than 100 years of white-light images stored in photographic plates and films that are available at Kodaikanal observatory starting from 1904. The images were digitized using a 4k × 4k format CCD-camera-based digitizer unit.The digitized images were calibrated for relative plate density and aligned in such a way that the solar north is in upward direction. A semi-automated sunspot detection technique was used to identify the sunspots on the digitized images.Results. In addition to describing the calibration procedure and availability of the data, we here present preliminary results on the sunspot area measurements and their variation with time. The results show that the white-light images have a uniform spatial resolution throughout the 90 years of observations. However, the contrast of the images decreases from 1968 onwards. The images are circular and do not show any major geometrical distortions. The measured monthly averaged sunspot areas closely match the Greenwich sunspot area over the four solar cycles studied here. The yearly averaged sunspot area shows a high degree of correlation with the Greenwich sunspot area. Though the monthly averaged sunspot number shows a good correlation with the monthly averaged sunspot areas, there is a slight anti-correlation between the two during solar maximum. Conclusions. The Kodaikanal data archive is hosted at http://kso.iiap.res.in. The long time sequence of the Kodaikanal whitelight images provides a consistent data set for sunspot areas and other proxies. Many studies can be performed using Kodaikanal data alone without requiring intercalibration between different data sources.

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Solar physics at Kodaikanal

Cited by 24 publications

References 2 publications

On the Weakening of the Chromospheric Magnetic Field in Active Regions

On the Weakening of the Chromospheric Magnetic Field in Active Regions

Network and plage indices from Kodaikanal Ca-K data

Digitized archive of the Kodaikanal images: Representative results of solar cycle variation from sunspot area determination

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