Solar differential rotation determined by tracing coronal bright points in SOHO-EIT images

Brajša, R.; Wöhl, H.; Vršnak, Bojan; Ruždjak, V.; Clette, F.; Hochedez, J.‐F.

doi:10.1051/0004-6361:20020945

Cited by 39 publications

(56 citation statements)

References 25 publications

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“…The numerical ROI parameters of the automatic method (sharpness of the subimages, their circumference range and the intensity range of their brightness) were chosen to resemble the interactive method as much as possible. The ROI parameters that were used in the actual analysis were given by Brajša et al (2002a). We point out that it is not possible to identify different tracer subtypes applying the automatic method.…”

Section: The Data Set and Reduction Methodsmentioning

confidence: 99%

“…Further technical details about data selection and preparation of images for the reduction were given in Brajša et al (2001a;2002a).…”

Section: The Data Set and Reduction Methodsmentioning

confidence: 99%

“…All measured rotation velocities (without any velocity filter, Brajša et al 2002a) with the corresponding mean values of the CMD are divided in 10-deg latitude bins. Now, for each latitude bin the mean value of the corrected rotation velocity ω and the parameter β are calculated according to Eqs.…”

Section: The Calculation Proceduresmentioning

confidence: 99%

“…The raw and corrected data for both methods of data reduction are further treated in the usual way, applying the two-step velocity filter (Brajša et al 2002a) and calculating the parameters of the solar differential rotation, A, B, and C according to the standard formula…”

Section: Differential Rotationmentioning

confidence: 99%

“…In Brajša et al (2002a) the results on differential rotation for the two methods, for the northern and southern solar hemispheres, and for the three subtypes of tracers (pointlike structures, small loops, and small active regions) were presented and compared. Properties of the solar velocity field indicated by motions of coronal bright points expressed through the rotation velocity residual, meridional motions and Reynolds stresses were discussed in Vršnak et al (2003).…”

Section: Introductionmentioning

confidence: 99%

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Height correction in the measurement of solar differential rotation determined by coronal bright points

Brajša¹,

Wöhl²,

Vršnak³

et al. 2004

A&A

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Abstract. Full-disc solar images obtained with the Extreme Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) are used to analyse solar differential rotation by tracing coronal bright points for the period June 4, 1998 to May 22, 1999. A method for the simultaneous determination of the true solar synodic rotation velocity and the height of the tracers is applied to data sets analysed with interactive and automatic methods. The calculated height of coronal bright points is on average 8000-12000 km above the photosphere. Corrected rotation velocities are transformed into sidereal ones and compared with results from the literature, obtained with various methods and tracers. The differential rotation profile determined by coronal bright points with the interactive method corresponds roughly to the profile obtained by correlating photospheric magnetic fields and the profile obtained from the automatic method corresponds roughly to the rotation of sunspot groups. This result is interpreted in terms of the differences obtained in the latitudinal distribution of coronal bright points using the two methods.

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Section: The Data Set and Reduction Methodsmentioning

confidence: 99%

“…Further technical details about data selection and preparation of images for the reduction were given in Brajša et al (2001a;2002a).…”

Section: The Data Set and Reduction Methodsmentioning

confidence: 99%

Section: The Calculation Proceduresmentioning

confidence: 99%

Section: Differential Rotationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Height correction in the measurement of solar differential rotation determined by coronal bright points

Brajša¹,

Wöhl²,

Vršnak³

et al. 2004

A&A

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On the solar rotation and activity

Brajša¹,

Wöhl

Ruždjak

et al. 2007

Astron Nachr

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Thei nteractionb etween differentialr otationa nd magnetic fieldsi nthe solar convectionz one wasr ecently modelledb y Brun ( 2004). Onec onsequence of that model is that theM axwells tresses can oppose theR eynolds stresses, and thus contribute to thet ransport of thea ngular momentum towards thes olar poles, leading to ar educed differentialr otation. So,when magnetic fieldsare weaker,amore pronounced differentialrotationcan be expected, yielding ahigher rotation velocity at lowlatitudes takenonthe average. This hypothesisisconsistent with thebehaviour of thesolar rotationduring theM aunder minimum. In this work we search for similars ignatures of ther elationshipb etween thes olar activity and rotationd etermined tracing sunspot groups and coronal bright points. We use thee xtended Greenwich datas et and as eries of full-discs olar images takena t2 8.4n mw ith theE IT instrument on theS OHO spacecraft (1998)(1999)(2000). We investigatethe dependence of thesolar rotationonthe solar activity (describedbythe relative sunspot number) andthe interplanetary magnetic field (calculatedfromthe interdiurnal variability index).Possible rotationalsignatures of twoweak solar activity cycles at thebeginning of the20thcentury (Gleissbergminimum) are discussed. The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set and a series of full-disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998)(1999)(2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed.

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Segmentation, Tracking and Characterization of Solar Features from EIT Solar Corona Images

2009

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With the multiplication of sensors and instruments, size, amount and quality of solar image data are constantly increasing, and analyzing this data requires defining and implementing accurate and reliable algorithms. In the context of solar features analysis, it is particularly important to accurately delineate their edges and track their motion, to estimate quantitative indices and analyse their evolution through time. Herein, we introduce an image processing pipeline that segment, track and quantify solar features from a set of multispectral solar corona images, taken with eit EIT instrument. We demonstrate the method on the automatic tracking of Active Regions from EIT images, and on the analysis of the spatial distribution of coronal bright points. The method is generic enough to allow the study of any solar feature, provided it can be segmented from EIT images or other sources.

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Solar differential rotation determined by tracing coronal bright points in SOHO-EIT images

Cited by 39 publications

References 25 publications

Height correction in the measurement of solar differential rotation determined by coronal bright points

Height correction in the measurement of solar differential rotation determined by coronal bright points

On the solar rotation and activity

Segmentation, Tracking and Characterization of Solar Features from EIT Solar Corona Images

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