Measurements of Solar Differential Rotation Using the Century Long Kodaikanal Sunspot Data

Jha, Bibhuti Kumar; Priyadarshi, Aditya; Mandal, Sudip; Chatterjee, Subhamoy; Banerjee, D.

doi:10.1007/s11207-021-01767-8

Cited by 20 publications

(25 citation statements)

References 39 publications

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“…The latitude-time plot for all these data sets are shown in Figure 2a (sunspot), 2b (plages), 2c (filaments) and 2d (Ca-k prominences). These digitized data sets have been extensively used (Mandal et al 2017(Mandal et al , 2020Jha et al 2019Jha et al , 2021 to study the various aspects of long-term solar variability. Recently, Mordvinov et al (2020) have reconstructed the magnetic butterfly diagram corresponding to the past cycle using the digitized data from KoSO.…”

Section: A Few Results From Koso Digital Archivementioning

confidence: 99%

Long-term Evolution of Magnetic Field Proxies as Deduced from Archival Data

Banerjee,

Jha,

Mandal

et al. 2022

Proc. IAU

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Regular observations of the solar magnetic field are available only for about the last five cycles. Thus, to understand the origin of the variation of the solar magnetic field, it is essential to reconstruct the magnetic field for the past cycles, utilizing the proxies of the magnetic field from other data sets. Long-term uniform observations for the past 100 yrs, as recorded at the Kodaikanal Solar Observatory (KoSO), in multi-wavelengths provide such an opportunity. Various automatic techniques have been developed to extract these features from KoSO data. We analyzed the properties of these extracted features to understand global solar magnetism in the past.

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Section: A Few Results From Koso Digital Archivementioning

confidence: 99%

Long-term Evolution of Magnetic Field Proxies as Deduced from Archival Data

Banerjee,

Jha,

Mandal

et al. 2022

Proc. IAU

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“…Typical values describing the Sun's surface rotation rate are given in Table 1, taken from Snodgrass (1983). Many studies have attempted to constrain the Sun's differential rotation profile (Newton & Nunn 1951;Wilcox & Howard 1970;Howard et al 1984;Beck 2000;Lamb 2017;Beljan et al 2017;Jha et al 2021), however the profile from Snodgrass (1983) features embedded there) rotating faster than the polar regions.…”

Section: Methodsmentioning

confidence: 99%

Accounting for differential rotation in calculations of the Sun’s angular momentum-loss rate

Finley¹,

Brun²

2023

A&A

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Context. Sun-like stars shed angular momentum due to the presence of magnetised stellar winds. Magnetohydrodynamic models have been successful in exploring the dependence of this "wind-braking torque" on various stellar properties, however the influence of surface differential rotation is largely unexplored. As the wind-braking torque depends on the rotation rate of the escaping wind, the inclusion of differential rotation should effectively modulate the angular momentum-loss rate based on the latitudinal variation of wind source regions.Aims. Here we aim to quantify the influence of surface differential rotation on the angular momentum-loss rate of the Sun, in comparison to the typical assumption of solid-body rotation. Methods. To do this, we exploit the dependence of the wind-braking torque on the effective rotation rate of the coronal magnetic field, which is known to be vitally important in magnetohydrodynamic models. This quantity is evaluated by tracing field lines through a Potential Field Source Surface (PFSS) model, driven by ADAPT-GONG magnetograms. The surface rotation rates of the open magnetic field lines are then used to construct an open-flux weighted rotation rate, from which the influence on the wind-braking torque can be estimated. Results. During solar minima, the rotation rate of the corona decreases with respect to the typical solid-body rate (the Carrington rotation period is 25.4 days), as the sources of the solar wind are confined towards the slowly-rotating poles. With increasing activity, more solar wind emerges from the Sun's active latitudes which enforces a Carrington-like rotation. Coronal rotation often displays a north-south asymmetry driven by differences in active region emergence rates (and consequently latitudinal connectivity) in each hemisphere.Conclusions. The effect of differential rotation on the Sun's current wind-braking torque is limited. The solar wind-braking torque is ∼ 10 − 15% lower during solar minimum, (compared with the typical solid body rate), and a few percent larger during solar maximum (as some field lines connect to more rapidly rotating equatorial latitudes). For more rapidly-rotating Sun-like stars, differential rotation may play a more significant role, depending on the configuration of the large-scale magnetic field.

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“…As a first step for the tracking algorithm, we identify BMRs following the method used in Jha et al (2020), which is based on the technique explained in Stenflo & Kosovichev (2012). Our tracking algorithm is based on the idea of sunspot tracking described in Jha et al (2021) with the needed modification in the case of BMRs.…”

Section: Data and Tracking Algorithmmentioning

confidence: 99%

Automatic Algorithm for Tracking Bipolar Magnetic Regions

Sreedevi,

Jha

2022

Proc. IAU

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Properties of bipolar magnetic regions (BMRs), particularly, the tilt angle play critical roles in generating the observed polar magnetic field and its reversal. Hence, a long-term study of BMR over its lifetime is crucial not only to understand the solar dynamo but also to identify the origin of the properties of BMR. In our work, we have developed an automatic algorithm to detect and track the BMRs from the line-of-sight (LOS) magnetograms of Michelson Doppler Imager (MDI) for the period of Solar Cycle 23 over its lifetime/disk passage. Here, we present the details of our algorithm and the features of BMR, particularly the tilt angle, magnetic field strength and lifetime.

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Measurements of Solar Differential Rotation Using the Century Long Kodaikanal Sunspot Data

Cited by 20 publications

References 39 publications

Long-term Evolution of Magnetic Field Proxies as Deduced from Archival Data

Long-term Evolution of Magnetic Field Proxies as Deduced from Archival Data

Accounting for differential rotation in calculations of the Sun’s angular momentum-loss rate

Automatic Algorithm for Tracking Bipolar Magnetic Regions

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