Tracing sunspot groups to determine angular momentum transfer on the Sun

Sudar, D.; Skokić, Ivica; Ruždjak, Domagoj; Brajša, R.; Wöhl, H.

doi:10.1093/mnras/stu099

Cited by 19 publications

(57 citation statements)

References 51 publications

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“…Another branch might be visible above 50 • , even though the errors are becoming large in that region of latitudes. This type of result is more consistent with Doppler measurements than with sunspot data where Sudar et al (2014) found no stable pattern that resembles torsional oscillations.…”

Section: Solar Rotation Profile and Rotation Velocity Residualssupporting

confidence: 88%

“…The only notable exception is the bin at 25 • where q ≈ −1500 m 2 s −2 and possibly the bin at 15 • . Sudar et al (2014) found the minimum at the same latitude, but about twice as deep. They also found negative values of q for all latitudes below 35 • .…”

Section: Horizontal Reynolds Stressmentioning

confidence: 78%

“…It is quite common to filter out such outliers by selecting a fixed range of acceptable rotational velocity (Brajša et al 2002b;Vršnak et al 2003;Sudar et al 2014Sudar et al , 2015. This approach neglects the fact that the solar rotation varies with latitude and that such a fixed cut-off does not have a uniform effect on all latitudes.…”

Section: Data and Reduction Methodsmentioning

confidence: 99%

“…In order not to detect false meridional flows due to uneven distribution of tracers across different latitudes, it is necessary to assign calculated velocities to the latitude of the first measurements of position for each CBP (Olemskoy & Kitchatinov 2005;Sudar et al 2014). As with Δv rot , it is wise to take a look at the distribution of meridional velocities, v mer (Fig.…”

Section: Meridional Velocitiesmentioning

confidence: 99%

“…The oldest known tracers for measuring the solar rotation profile are sunspots, which have been used for a long time (Newton & Nunn 1951;Howard et al 1984;Balthasar et al 1986;Brajša et al 2002a;Sudar et al 2014). The biggest advantage of sunspots is that they have been observed for more than a century.…”

Section: Introductionmentioning

confidence: 99%

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Meridional motions and Reynolds stress from SDO/AIA coronal bright points data

Sudar

Saar

Skokić

et al. 2016

A&A

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Context. It is possible to detect and track coronal bright points (CBPs) in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) images. A combination of high resolution and high cadence provides a wealth of data that can be used to determine velocity flows on the solar surface with very high accuracy. Aims. We derived a very accurate solar rotation profile and investigated meridional flows, torsional oscillations, and horizontal Reynolds stress based on ≈6 months of SDO/AIA data. Methods. We used a segmentation algorithm to detect CBPs in SDO/AIA images. We also used invariance of the solar rotation profile with central meridian distance (CMD) to determine the height of CBPs in the 19.3 nm channel. Results. The best fit solar rotation profile is given by ω(b) = (14.4060 ± 0.0051 + (−1.662 ± 0.050) sin 2 b + (−2.742 ± 0.081) sin 4 b) • day −1 . The height of CBPs in the SDO/AIA 19.3 nm channel was found to be ≈6500 km. Meridional motion is predominantly poleward for all latitudes, while solar velocity residuals show signs of torsional oscillations. Horizontal Reynolds stress was found to be smaller than in similar works, but still showed transfer of angular momentum towards the solar equator. Conclusions. Most of the results are consistent with Doppler measurements rather than tracer measurements. The fairly small calculated value of horizontal Reynolds stress might be due to the particular phase of the solar cycle. Accuracy of the calculated rotation profile indicates that it is possible to measure changes in the profile as the solar cycle evolves. Analysis of further SDO/AIA CBP data will also provide a better understanding of the temporal behaviour of the rotation velocity residuals, meridional motions, and Reynolds stress.

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Section: Solar Rotation Profile and Rotation Velocity Residualssupporting

confidence: 88%

Section: Horizontal Reynolds Stressmentioning

confidence: 78%

Section: Data and Reduction Methodsmentioning

confidence: 99%

Section: Meridional Velocitiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Meridional motions and Reynolds stress from SDO/AIA coronal bright points data

Sudar

Saar

Skokić

et al. 2016

A&A

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The Solar Rotation in the Period 1853 – 1870 from the Sunspot Catalogues of Carrington, Peters, and de la Rue

Casas

Vaquero

2015

Sol Phys

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R. C. Carrington, C. H. F. Peters, and W. de la Rue observed the sunspots in the second half of the 19th century, determining their heliographic positions between 1853 and 1870, before the establishment of the solar program of the Royal Greenwich Observatory. The large tables of sunspot positions included in the catalogues published by these observers have recently been converted to a machine readable format. The present work analyses this data by calculating the sunspot group velocities for each observer. These results are then fitted with a differential rotation law to compare the data of the three observers with each other and with the results published by other authors. Finally, a study is made of the possible relationship between the sunspot group areas as determined by de la Rue and the corresponding sunspot group velocities.

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Meridional Motion and Reynolds Stress from Debrecen Photoheliographic Data

et al. 2017

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The Debrecen Photoheliographic Data catalogue is a continuation of the Greenwich Photoheliographic Results providing daily positions of sunspots and sunspot groups. We analyse the data for sunspot groups focusing on meridional motions and transfer of angular momentum towards the solar equator. Velocities are calculated with a daily shift method including an automatic iterative process of removing the outliers. Apart from the standard differential rotation profile, we find meridional motion directed towards the zone of solar activity. The difference in measured meridional flow in comparison to Doppler measurements and some other tracer measurements is interpreted as a consequence of different flow patterns inside and outside of active regions. We also find a statistically significant dependence of meridional motion on rotation velocity residuals confirming the transfer of angular momentum towards the equator.

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Tracing sunspot groups to determine angular momentum transfer on the Sun

Cited by 19 publications

References 51 publications

Meridional motions and Reynolds stress from SDO/AIA coronal bright points data

Meridional motions and Reynolds stress from SDO/AIA coronal bright points data

The Solar Rotation in the Period 1853 – 1870 from the Sunspot Catalogues of Carrington, Peters, and de la Rue

Meridional Motion and Reynolds Stress from Debrecen Photoheliographic Data

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