Variation of Supergranule Parameters with Solar Cycles: Results from Century-long Kodaikanal Digitized Ca ii K Data

Chatterjee, Subhamoy; Mandal, Sudip; Banerjee, D.

doi:10.3847/1538-4357/aa709d

Cited by 21 publications

(24 citation statements)

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“…The latter was proposed by, e.g., Crouch et al (2007), who sug- gested that random clustering of magnetic elements could trigger downflows on supergranulation scales. Recently, Chatterjee et al (2017) found evidence for a solar-cycle dependence of supergranular parameters (e.g., the cell size) in century-long Ca ii K observation records.…”

Section: Cork Simulationmentioning

confidence: 99%

Evolution and wave-like properties of the average solar supergranule

Langfellner

Birch

Gizon

2018

A&A

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Context. Solar supergranulation presents us with many mysteries. For example, previous studies in spectral space found that supergranulation has wave-like properties. Aims. Here we study, in real space, the wave-like evolution of the average supergranule over a range of spatial scales (from 10 to 80 Mm). We complement this by characterizing the evolution of the associated network magnetic field. Methods. We use one year of data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory to measure horizontal near-surface flows near the solar equator by applying time-distance helioseismology (TD) on Dopplergrams and granulation tracking (LCT) on intensity images. The average supergranule outflow (or inflow) is constructed by averaging over 10,000 individual outflows (or inflows). The contemporaneous evolution of the magnetic field is studied with HMI line-of-sight observations. Results. We confirm and extend previous measurements of the supergranular wave dispersion relation to angular wavenumbers in the range 50 < kR < 270. We find a plateau for kR > 120. In real space, larger supergranules undergo oscillations with longer periods and lifetimes than smaller cells. We find excellent agreement between TD and LCT and obtain wave properties that are independent of the tracking rate. The observed network magnetic field follows the oscillations of the supergranular flows with a six-hour time lag. This behavior can be explained by computing the motions of corks carried by the supergranular flows. Conclusions. Signatures of supergranular waves in surface horizontal flows near the solar equator can be observed in real space. These oscillatory flows control the evolution of the network magnetic field, in particular they explain the recently discovered eastwest anisotropy of the magnetic field around the average supergranule. Background flow measurements that we obtain from Doppler frequency shifts do not favor shallow models of supergranulation.

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Section: Cork Simulationmentioning

confidence: 99%

Evolution and wave-like properties of the average solar supergranule

Langfellner

Birch

Gizon

2018

A&A

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“…Antonucci et al 1977;Ermolli et al 2009b;Dorotovic et al 2010;Chatzistergos et al 2016Chatzistergos et al , 2019bBarata et al 2018;Tlatov & Tlatova 2019, and references therein), the solar radius variations (Meftah et al 2018;Hiremath et al 2020), network cell properties (e.g. Berrilli et al 1999;Ermolli et al 2003;Chatterjee et al 2017;Raju 2018), photometric properties of disc features over the solar cycle (e.g. Ermolli et al 2007Ermolli et al , 2010, as well as for the purpose of reconstructing of irradiance variations (e.g.…”

Section: Introductionmentioning

confidence: 99%

Analysis of full-disc Ca II K spectroheliograms

Chatzistergos

Ermolli

Krivova

et al. 2020

A&A

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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.

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“…In recent years, digitisation of various archives (for a list of the available archives see Chatzistergos 2017) allowed starting extensive exploitation of historical Ca II K spectroheliograms (SHG, e.g. Ribes & Mein 1985;Kariyappa & Pap 1996;Foukal 1996Foukal , 1998Caccin et al 1998;Worden et al 1998;Zharkova et al 2003;Lefebvre et al 2005;Ermolli et al 2009a,b;Tlatov et al 2009;Bertello et al 2010;Dorotovič et al 2010;Sheeley et al 2011;Priyal et al 2014Priyal et al , 2017Chatterjee et al 2016Chatterjee et al , 2017. Overall, there are numerous published results from historical Ca II K images, which agree in some respects, but also show significant differences (see Ermolli et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Analysis of full disc Ca II K spectroheliograms

Chatzistergos

Ermolli

Krivova

et al. 2019

A&A

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Context. Reconstructions of past irradiance variations require suitable data on solar activity. The longest direct proxy is the sunspot number, and it has been most widely employed for this purpose. These data, however, only provide information on the surface magnetic field emerging in sunspots, while a suitable proxy of the evolution of the bright magnetic features, specifically faculae/plage and network, is missing. This information can potentially be extracted from the historical full-disc observations in the Ca II K line. Aims. We use several historical archives of full-disc Ca II K observations to derive plage areas over more than a century. Employment of different datasets allows the identification of systematic effects in the images, such as changes in instruments and procedures, as well as an assessment of the uncertainties in the results. Methods. We have analysed over 100 000 historical images from eight digitised photographic archives of the Arcetri, Kodaikanal, McMath-Hulbert, Meudon, Mitaka, Mt Wilson, Schauinsland, and Wendelstein observatories, and one archive of modern observations from the Rome/PSPT. The analysed data cover the period 1893–2018. We first performed careful photometric calibration and compensation for the centre-to-limb variation, and then segmented the images to identify plage regions. This has been consistently applied to both historical and modern observations. Results. The plage series derived from different archives are generally in good agreement with each other. However, there are also clear deviations that most likely hint at intrinsic differences in the data and their digitisation. We showed that accurate image processing significantly reduces errors in the plage area estimates. Accurate photometric calibration also allows precise plage identification on images from different archives without the need to arbitrarily adjust the segmentation parameters. Finally, by comparing the plage area series from the various records, we found the conversion laws between them. This allowed us to produce a preliminary composite of the plage areas obtained from all the datasets studied here. This is a first step towards an accurate assessment of the long-term variation of plage regions.

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Variation of Supergranule Parameters with Solar Cycles: Results from Century-long Kodaikanal Digitized Ca ii K Data

Cited by 21 publications

References 24 publications

Evolution and wave-like properties of the average solar supergranule

Evolution and wave-like properties of the average solar supergranule

Analysis of full-disc Ca II K spectroheliograms

Analysis of full disc Ca II K spectroheliograms

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