Long-term Evolution of the Sun’s Magnetic Field during Cycles 15–19 Based on Their Proxies from Kodaikanal Solar Observatory

Мордвинов, А. В.; Karak, Bidya Binay; Banerjee, D.; Chatterjee, Subhamoy; Golubeva, E. M.; Khlystova, A. I.

doi:10.3847/2041-8213/abba80

Cited by 14 publications

(7 citation statements)

References 31 publications

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“…The synthesized magnetograms shown in Figure 7 confirm the broad predictions made previously by Mordvinov et al (2020) but give greater detail. Indeed the detail is now good enough for a plausible analysis of the causes and effects of individual poleward surges, of the kind carried out for actual magnetograph data (Lockwood et al, 2017;Mordvinov and Kitchatinov, 2019;Mordvinov et al, 2021).…”

Section: Discussionsupporting

confidence: 85%

“…These are determined from the WSO data for solar cycles 20-24 and the dates for cycle 19 were obtained from Babcock (1959) and Babcock (1961). For cycles 15-18 we use the dates derived by Mordvinov et al (2020) from historic observations at the Kodaikanal Solar Observatory (KoSO) (see also Thomas et al, 2014). Mordvinov et al (2020) estimate the polar magnetic field using the synoptic observations of the Sun's emission in the CaIIK and Hα spectral lines, using the fact that the CaIIK intensity correlates well with the unsigned magnetic flux, while the sign of the flux is derived from the corresponding Hα data that provides the information of the spatial maps of dominant field polarity because Hα filaments and filament channels mark out polarity inversion lines.…”

Section: Polar Faculaementioning

confidence: 99%

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Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 2. Solar observations

Lockwood

Owens

Yardley

et al. 2022

Front. Astron. Space Sci.

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We study historic observations of solar activity from the 20th-century rise towards the peak of the Modern Grand Solar Maximum (MGSM) and compare with observations of the decline that has occurred since. The major difference in available solar observations of the rise and of the fall are accurate magnetograms from solar magnetographs: we here use synthetic magnetograms to interpret the rise and employ historic observations of Polar Crown Filaments to test them and verify their use. We show that eclipse images at sunspot minimum reveal the long-term variation of open flux deduced from geomagnetic observations in Paper 1 (Lockwood et al., 2022). We also make use of polar coronal hole fluxes derived from historic white light images of polar faculae, but have to consider the implications of the fact that these facular images do not tell us the polarity of the field. Given this caveat, the agreement between the polar coronal hole fluxes and the values derived from open flux continuity modelling based on sunspot numbers is extremely good. This comparison indicates that one possible solution to the “open flux problem” is open flux within the streamer belt that potential-based modelling of coronal fields from photospheric fields is not capturing. We take a detailed look at the solar cycle at the peak of the MGSM, cycle 19, and show the variation of the polar coronal hole fluxes and the inferred poleward flux surges are predictable from the asymmetries in flux emergence in the two hemispheres with implied transequatorial flux transfer and/or “anti-Hale” (or more general “rogue” active region flux) emergence late in the sunspot cycle.

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Section: Discussionsupporting

confidence: 85%

Section: Polar Faculaementioning

confidence: 99%

Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 2. Solar observations

Lockwood

Owens

Yardley

et al. 2022

Front. Astron. Space Sci.

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“…Similarly, Mordvinov et al (2020) reconstructed magnetograms over 1907-1965 from Kodaikanal Ca II K Carrington maps produced by Chatterjee et al (2016). They used a polynomial relationship between the magnetic flux density and Ca II K contrast.…”

Section: Connection Between Ca II K Brightness and Magnetic Field Str...mentioning

confidence: 99%

Full-disc Ca ii K observations—A window to past solar magnetism

Chatzistergos

Krivova

Ermolli

2022

Front. Astron. Space Sci.

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Full-disc observations of the Sun in the Ca ii K line provide one of the longest collections of solar data. First such observations were made in 1892 and since then various sites around the world have carried out regular observations, with Kodaikanal, Meudon, Mt Wilson, and Coimbra being some of the most prominent ones. By now, Ca ii K observations from over 40 different sites allow an almost complete daily coverage of the last century. Ca ii K images provide direct information on plage and network regions on the Sun and, through their connection to solar surface magnetic field, offer an excellent opportunity to study solar magnetism over more than a century. This makes them also extremely important, among others, for solar irradiance reconstructions and studies of the solar influence on Earth’s climate. However, these data also suffer from numerous issues, which for a long time have hampered their analysis. Without properly addressing these issues, Ca ii K data cannot be used to their full potential. Here, we first provide an overview of the currently known Ca ii K data archives and sources of the inhomogeneities in the data, before discussing existing processing techniques, followed by a recap of the main results derived with such data so far.

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“…Recently, Mordvinov et al (2020) reconstructed the solar magnetic field using the Sun's emission in the CaII K and H𝛼 lines from KoSO. This reconstruction enabled us to study the evolution of solar magnetic field and reversals in Cycles 15-19.…”

Section: Introductionmentioning

confidence: 99%

Evolution of the Sun’s Polar Fields and the Poleward Transport of Remnant Magnetic Flux

Мордвинов

Kitchatinov

2019

Sol Phys

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Synoptic magnetograms and relevant proxy data were analyzed to study the evolution of the Sun's polar magnetic fields. Time-latitude analysis of large-scale magnetic fields demonstrates cyclic changes in their zonal structure and the polar-field buildup. The time-latitude distributions of the emergent and remnant magnetic flux enable us to examine individual features of recent cycles. The poleward transport of predominantly following polarities contributed much of the polar flux and led to polar-field reversals. Multiple reversals of dominant polarities at the Sun's poles were identified in Cycles 20 and 21. Three-fold reversals were caused by remnant flux surges of following and leading polarities. Time-latitude analysis of solar magnetic fields in Cycles 20-24 revealed zones which are characterized by a predominance of negative (non-Joy's) tilts and appearance of active regions which violate Hale's polarity law. The decay of non-Joy's and anti-Hale's active regions result in remnant flux surges which disturb the usual order in magnetic flux transport and sometimes lead to multiple reversals of polar fields. The analysis of local and large-scale magnetic fields in their causal relation improved our understanding of the Sun's polar field weakening.

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Long-term Evolution of the Sun’s Magnetic Field during Cycles 15–19 Based on Their Proxies from Kodaikanal Solar Observatory

Cited by 14 publications

References 31 publications

Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 2. Solar observations

Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 2. Solar observations

Full-disc Ca ii K observations—A window to past solar magnetism

Evolution of the Sun’s Polar Fields and the Poleward Transport of Remnant Magnetic Flux

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