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

Chatzistergos, Theodosios; Ermolli, I.; Solanki, S. K.; Krivova, N. A.; Banerjee, D.; Jha, Bibhuti Kumar; Chatterjee, Subhamoy

doi:10.1007/s11207-019-1532-5

Cited by 20 publications

(19 citation statements)

References 30 publications

(90 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We note that over SC 23 the plage areas in all backbone series except the RP1 exhibit a secondary peak around 2004. This is attributed to the Ko data over that period as was also mentioned by Chatzistergos et al (2019c). Figure 9 shows the final composite 2 produced by merging the RP1 and the average historical backbones as well as the plage area composite obtained in Paper II for comparison.…”

Section: Plage Areas Compositementioning

confidence: 68%

“…1. More details on: the processing of the Ar, MM, MD1, Mi1, MW, RP1, Sc, and WS datasets can be found in Paper II; on processing the CT and Ro datasets in Chatzistergos et al (2019a); Ko in Chatzistergos et al (2019c); and Ky and SP in Chatzistergos et al (2020).…”

Section: Methodsmentioning

confidence: 99%

“…In this study, we present a plage area composite obtained on the basis of the results from 38 datasets. These include the data from the 16-bit digitisation of the Ko dataset (Chatzistergos et al 2019c) as well as the recently recovered data from the 16-bit digitisation of MW. Furthermore, we use a different methodology to create our plage area composite series, employing the "backbone" approach (Svalgaard & Schatten 2016;Chatzistergos et al 2017).…”

Section: Plage Areas Compositementioning

confidence: 99%

See 2 more Smart Citations

Analysis of full-disc Ca II K spectroheliograms

Chatzistergos

Ermolli

Krivova

et al. 2020

A&A

Self Cite

View full text Add to dashboard Cite

Context. Studies of long-term solar activity and variability require knowledge of the past evolution of the solar surface magnetism. The archives of full-disc Ca II K observations that have been performed more or less regularly at various sites since 1892 can serve as an important source of such information. Aims. We derive the plage area evolution over the last 12 solar cycles by employing data from all Ca II K archives that are publicly available in digital form, including several as-yet-unexplored Ca II K archives. Methods. We analysed more than 290 000 full-disc Ca II K observations from 43 datasets spanning the period between 1892–2019. All images were consistently processed with an automatic procedure that performs the photometric calibration (if needed) and the limb-darkening compensation. The processing also accounts for artefacts affecting many of the images, including some very specific artefacts, such as bright arcs found in Kyoto and Yerkes data. Our employed methods have previously been tested and evaluated on synthetic data and found to be more accurate than other methods used in the literature to treat a subset of the data analysed here. Results. We produced a plage area time-series from each analysed dataset. We found that the differences between the plage areas derived from individual archives are mainly due to the differences in the central wavelength and the bandpass used to acquire the data at the various sites. We empirically cross-calibrated and combined the results obtained from each dataset to produce a composite series of plage areas. The ’backbone’ approach was used to bridge the series together. We have also shown that the selection of the backbone series has little effect on the final composite of the plage area. We quantified the uncertainty of determining the plage areas with our processing due to shifts in the central wavelength and found it to be less than 0.01 in fraction of the solar disc for the average conditions found on historical data. We also found the variable seeing conditions during the observations to slightly increase the plage areas during the activity maxima. Conclusions. We provide the most complete so far time series of plage areas based on corrected and calibrated historical and modern Ca II K images. Consistent plage areas are now available on 88% of all days from 1892 onwards and on 98% from 1907 onwards.

show abstract

Section: Plage Areas Compositementioning

confidence: 68%

Section: Methodsmentioning

confidence: 99%

Section: Plage Areas Compositementioning

confidence: 99%

See 1 more Smart Citation

Analysis of full-disc Ca II K spectroheliograms

Chatzistergos

Ermolli

Krivova

et al. 2020

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…An accurate photometric calibration of this series was made by Chatzistergos et al () to make the data set ready for irradiance calculation and also detection of plages (Chatzistergos, Ermolli, Krivova, et al, ). Recently, the 16‐bit series was studied by Chatzistergos, Ermolli, Solanki, et al () confirming its superiority over the 8‐bit series in terms of uniformity. It is the same instrument which was used to make the disc‐blocked Ca II K spectroheliograms as well.…”

Section: Data Descriptionmentioning

confidence: 93%

Time‐Latitude Distribution of Prominences for 10 Solar Cycles: A Study Using Kodaikanal, Meudon, and Kanzelhohe Data

Chatterjee

Hegde

Banerjee

et al. 2020

Earth and Space Science

Self Cite

View full text Add to dashboard Cite

Solar prominences are structures of importance because of their role in polar field reversal. We study the long‐term variation of the time latitude distribution of solar prominences in this article. To accomplish this, we primarily used the digitized disc‐blocked Ca II K spectroheliograms as recorded from Kodaikanal Solar Observatory for the period of 1906–2002. For improving the data statistics we included full disc H α images from Meudon and Kanzelhohe Observatory, which are available after 1980. We developed an automated technique to identify the latitudinal locations of prominences in daily images from all three data sets. Derived time‐latitude distribution clearly depicted poleward migration of prominence structures for 10 cycles (15–24). Unlike previous studies, we separated the rate of poleward migration during onset and near pole, using piece‐wise linear fits. In most cases, we found acceleration in poleward migration with the change occurring near ±70° latitudes. The derived migration rates for such large number of solar cycles can provide important inputs toward understanding polar field buildup process.

show abstract

“…Willis et al, 2016;Pal et al, 2020), could allow irradiance reconstructions from properly calibrated historical Ca II K observations, e.g. those from Meudon (Malherbe & Dalmasse, 2019) or Kodaikanal (Chatzistergos et al, 2019c) observatories, to extend the reconstruction back to 1892 (Chatzistergos et al, 2020a).…”

Section: Discussionmentioning

confidence: 99%

Modelling solar irradiance from ground-based photometric observations

Chatzistergos

Ermolli

Giorgi

et al. 2020

J. Space Weather Space Clim.

Self Cite

View full text Add to dashboard Cite

Total solar irradiance (TSI) has been monitored from space since 1978, i.e. for about four solar cycles. The measurements show a prominent variability in phase with the solar cycle, as well as fluctuations on timescales shorter than a few days. However, the measurements were done by multiple and usually relatively short-lived missions. The different absolute calibrations of the individual instruments and the unaccounted for instrumental trends make estimates of the possible long-term trend in the TSI highly uncertain. Furthermore, both the variability and the uncertainty are strongly wavelength-dependent. While the variability in the UV irradiance is clearly in-phase with the solar cycle, the phase of the variability in the visible range has been debated. In this paper, we aim at getting an insight into the long-term trend of TSI since 1996 and the phase of the solar irradiance variations in the visible part of the spectrum. We use independent ground-based full-disc photometric observations in Ca II K and continuum from the Rome and San Fernando observatories to compute the TSI since 1996. We follow the empirical San Fernando approach based on the photometric sum index. We find a weak declining trend in the TSI of $ {-7.8}_{-0.8}^{+4.9}\times 1{0}^{-3}$ Wm−2 y−1 between the 1996 and 2008 activity minima, while between 2008 and 2019 the reconstructed TSI shows no trend to a marginally decreasing (but statistically insignificant) trend of $ {-0.1}_{-0.02}^{+0.25}\times 1{0}^{-3}$ Wm−2 y−1. The reference TSI series used for the reconstruction does not significantly affect the determined trend. The variation in the blue continuum (409.2 nm) is rather flat, while the variation in the red continuum (607.1 nm) is marginally in anti-phase, although this result is extremely sensitive to the accurate assessment of the quiet Sun level in the images. These results provide further insights into the long-term variation of the TSI. The amplitude of the variations in the visible is below the uncertainties of the processing, which prevents an assessment of the phase of the variations.

show abstract

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

Cited by 20 publications

References 30 publications

Analysis of full-disc Ca II K spectroheliograms

Analysis of full-disc Ca II K spectroheliograms

Time‐Latitude Distribution of Prominences for 10 Solar Cycles: A Study Using Kodaikanal, Meudon, and Kanzelhohe Data

Modelling solar irradiance from ground-based photometric observations

Contact Info

Product

Resources

About