Reconstructing solar magnetic fields from historical observations

Pevtsov, Alexei A.; Virtanen, Ilpo; Мурсула, К.; Tlatov, A. G.; Bertello, L.

doi:10.1051/0004-6361/201526620

Cited by 54 publications

(67 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus this area-scaled butterfly diagram provides some additional information for a greater time-span (1907-2007), in contrast to the super synoptic map presented in Sheeley et al (2011) with a study period between 1915 and 1985. The location pf overlap between the plage structures and magnetic patches in turn validated the theoretical expectation of a higher field strength being correlated with less Ca II K absorption (Pevtsov et al 2016). Therefore, the century-long Ca II K data can act as a proxy for understanding the locational evolution of magnetic patches.…”

Section: Resultssupporting

confidence: 66%

See 1 more Smart Citation

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

Chatterjee

Banerjee

Ravindra

2016

ApJ

View full text Add to dashboard Cite

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.

show abstract

Section: Resultssupporting

confidence: 66%

“…Recently Pevtsov et al (2016) have attempted to create a homogeneous, long term series of pseudomagnetograms using a combination of Ca II K line images and sunspot polarity measurements. We hope to pursue the same in the near future for our KSO data.…”

mentioning

confidence: 99%

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

Chatterjee

Banerjee

Ravindra

2016

ApJ

View full text Add to dashboard Cite

show abstract

“…The issue of the low spatial resolution of the Ca 854.2 nm line was mentioned by Pevtsov et al (2016) based on the findings of Leenaarts et al (2006). The reported reversal of the relation at high magnetic fluxes with the Ca II K data, as well as the lack of correlation for the Ca II infrared data considered by Pevtsov et al (2016), is perfectly consistent with the inclusion of sunspots in their analysis. The large scatter is possibly due to the narrower nominal bandwidth of Mt Wilson data (0.35 Å) compared to that of the Rome/PSPT (2.5 Å).…”

Section: Comparison To Results From the Literaturementioning

confidence: 76%

Recovering the unsigned photospheric magnetic field from Ca II K observations

Chatzistergos

Ermolli

Solanki

et al. 2019

A&A

View full text Add to dashboard Cite

Context.A number of studies have aimed at defining the exact form of the relation between magnetic field strength and Ca II H and K core brightness. All previous studies have, however, been restricted to isolated regions on the solar disc or to a limited set of observations. Aims. We reassess the relationship between the photospheric magnetic field strength and the Ca II K intensity for a variety of surface features as a function of the position on the disc and the solar activity level. This relationship can be used to recover the unsigned photospheric magnetic field from images recorded in the core of Ca II K line. Methods. We have analysed 131 pairs of high-quality, full-disc, near-co-temporal observations from the Helioseismic and Magnetic Imager (SDO/HMI) and Precision Solar Photometric Telescope (Rome/PSPT) spanning half a solar cycle. To analytically describe the observationally-determined relation, we considered three different functions: a power law with an offset, a logarithmic function, and a power law function of the logarithm of the magnetic flux density. We used the obtained relations to reconstruct maps of the line-of-sight component of the unsigned magnetic field (unsigned magnetograms) from Ca II K observations, which were then compared to the original magnetograms. Results. We find that both power-law functions represent the data well, while the logarithmic function is good only for quiet periods. We see no significant variation over the solar cycle or over the disc in the derived fit parameters, independently of the function used. We find that errors in the independent variable, usually not accounted for, introduce attenuation bias. To address this, we binned the data with respect to the magnetic field strength and Ca II K contrast separately and derived the relation for the bisector of the two binned curves. The reconstructed unsigned magnetograms show good agreement with the original ones. RMS differences are less than 90 G. The results were unaffected by the stray-light correction of the SDO/HMI and Rome/PSPT data. Conclusions. Our results imply that Ca II K observations, accurately processed and calibrated, can be used to reconstruct unsigned magnetograms by using the relations derived in our study.

show abstract

“…Schrijver & Harvey (1989) also derived an integrated chromospheric emission from low-resolution synoptic maps and concluded that power laws describing local relationships led to similar power laws describing the so-called flux-flux (between disk-integrated variables) relationships. Conversely, Pevtsov et al (2016) used Ca synoptic maps to reconstruct pseudo-magnetograms.…”

Section: Observational Inputsmentioning

confidence: 99%

Solar chromospheric emission and magnetic structures from plages to intranetwork: Contribution of the very quiet Sun

Meunier

2018

A&A

View full text Add to dashboard Cite

Context. We need to establish a correspondence between the magnetic structures generated by models and usual stellar activity indexes to simulate radial velocity time series for stars less active than the Sun. This is necessary to compare the outputs of such models with observed radial velocity jitters and is critical to better understand the impact of stellar activity on exoplanet detectability. Aims. We propose a coherent picture to describe the relationship between magnetic activity, including the so-called quiet Sun regions, and the chromospheric emission using the Sun as a test-bench and a reference. Methods. We analyzed a long time series of Michelson Doppler imaging (MDI) magnetograms jointly with chromospheric emission time series obtained at Sacramento Peak and Kitt Peak observatories. This has allowed us to study the variability in the quiet Sun over the solar cycle, and then, based on available relations between magnetic fields in active structures and chromospheric emission, to propose an empirical reconstruction of the solar chromospheric emission based on all contributions. Results. We show that the magnetic flux covering the solar surface, including in the quieted regions, varies in phase with the solar cycle, suggesting a long-term relationship between the global dynamo and the contribution of all components of solar activity. We have been able to propose a reconstruction of the solar S-index, including a relationship between the weak field component and its chomospheric emission, which is in good agreement with the literature. This allows us to explain that stars with a low average chromospheric emission level exhibit a low variability. Conclusions. We conclude that weak flux regions significantly contribute to the chromospheric emission; these regions should be critical in explaining the lower variability associated with the lower average activity level in other stars as compared to the Sun and estimated from their chromospheric emission.

show abstract

Reconstructing solar magnetic fields from historical observations

Cited by 54 publications

References 50 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

Recovering the unsigned photospheric magnetic field from Ca II K observations

Solar chromospheric emission and magnetic structures from plages to intranetwork: Contribution of the very quiet Sun

Contact Info

Product

Resources

About