Recovering Joy’s Law as a Function of Solar Cycle, Hemisphere, and Longitude

McClintock, Bruce; Norton, A. A.

doi:10.1007/s11207-013-0338-0

Cited by 77 publications

(75 citation statements)

References 31 publications

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“…A model for preferred longitudes, as exhibited by activity complexes (see 1 An error in the tilt angle analysis of Dasi-Espuig et al (2010) was pointed out by Ivanov (2012), and corrected by Dasi-Espuig et al (2013), where an anti-correlation remained in the normalized Kodaikanal sunspot tilt angles for cycles 15 -21 that they analyzed, and in weakened form in the MWO data. McClintock and Norton (2013) confirmed the existence of this correlation in the MWO data overall, but found that there was no correlation in the northern hemisphere, only in the southern hemisphere. Section 4.5), was also included.…”

Section: Unusual Cycle 23 Minimumsupporting

confidence: 60%

“…They did not report a change of mean tilt angle over the cycle. Stenflo and Kosovichev (2012) have analyzed the Joy's law tilt angle of selected magnetic bipoles over time and found no statistical change in average Joy's law tilts, and Li and Ulrich (2012) found from a long-term study that tilt angles of spots appear largely invariant with respect to time at a given latitude, but they decrease slowly during each cycle following the butterfly diagram (see McClintock and Norton, 2013, on the difficulty and complexity of sunspot tilt measurements).…”

Section: Unusual Cycle 23 Minimummentioning

confidence: 99%

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Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

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This review describes observations of the polar magnetic fields, models for the cyclical formation and decay of these fields, and evidence of their great influence in the solar atmosphere. The polar field distribution dominates the global structure of the corona over most of the solar cycle, supplies the bulk of the interplanetary magnetic field via the polar coronal holes, and is believed to provide the seed for the creation of the activity cycle that follows. A broad observational knowledge and theoretical understanding of the polar fields is therefore an essential step towards a global view of solar and heliospheric magnetic fields. Analyses of both high-resolution and long-term synoptic observations of the polar fields are summarized. Models of global flux transport are reviewed, from the initial phenomenological and kinematic models of Babcock and Leighton to present-day attempts to produce time-dependent maps of the surface magnetic field and to explain polar field variations, including the weakness of the cycle 23 polar fields. The relevance of the polar fields to solar physics extends far beyond the surface layers from which the magnetic field measurements usually derive. As well as discussing the polar fields' role in the interior as seed fields for new solar cycles, the review follows their influence outward to the corona and heliosphere. The global coronal magnetic structure is determined by the surface magnetic flux distribution, and is dominated on large scales by the polar fields. We discuss the observed effects of the polar fields on the coronal hole structure, and the solar wind and ejections that travel through the atmosphere. The review concludes by identifying gaps in our knowledge, and by pointing out possible future sources of improved observational information and theoretical understanding of these fields. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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Section: Unusual Cycle 23 Minimumsupporting

confidence: 60%

Section: Unusual Cycle 23 Minimummentioning

confidence: 99%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

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“…From the lack of dependence of the tilt angle on magnetic flux and because after the emergence stops the Coriolis force vanishes yet the bipoles do not appear to relax to the E-W direction but (statistically) to Joy's law, Kosovichev and Stenflo (2008) conclude that "Joy's law reflects not the dynamics of the rising flux tubes but the spiral orientation of the toroidal magnetic field lines below the surface as suggested by Babcock (1961)". As mentioned above, McClintock and Norton (2013) have endorsed this suggestion.…”

Section: Tilt Anglementioning

confidence: 72%

“…The latter, corrected relation, also fits the graph shown by Wang and Sheeley Jr (1991) in their Figure 1, in which sine tilt angle against sine latitude are plotted. It is noteworthy, that recently McClintock and Norton (2013) have used the corrected relation for Joy's law when citing the relations established by Wang and Sheeley Jr (1991) and Leighton (1969). The latter was based on tilt measurements by Brunner (1930), and plotted in Figure 7, right panel.…”

Section: Tilt Anglementioning

confidence: 99%

“…They found that tilt did not relax to zero, as one would expect from an E-W toroidal field and tilt imparted by the Coriolis force, which should cease once the top of the flux tube has fully emerged. Most recently, McClintock and Norton (2013) argued that Joy's law is due to a combination of both the Coriolis force acting on the rising flux as well as an initial tilt imparted to the flux rope from the toroidal geometry that it retains.…”

Section: Tilt Anglementioning

confidence: 99%

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Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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Digitization of sunspot drawings by Spörer made in 1861–1894

2015

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-history and philosophy of astronomy Most of our knowledge about the Sun's activity cycle arises from sunspot observations over the last centuries since telescopes have been used for astronomy. The German astronomer Gustav Spörer observed almost daily the Sun from 1861 until the beginning of 1894 and assembled a 33-year collection of sunspot data covering a total of 445 solar rotation periods. These sunspot drawings were carefully placed on an equidistant grid of heliographic longitude and latitude for each rotation period, which were then copied to copper plates for a lithographic reproduction of the drawings in astronomical journals. In this article, we describe in detail the process of capturing these data as digital images, correcting for various effects of the aging print materials, and preparing the data for contemporary scientific analysis based on advanced image processing techniques. With the processed data we create a butterfly diagram aggregating sunspot areas, and we present methods to measure the size of sunspots (umbra and penumbra) and to determine tilt angles of active regions. A probability density function of the sunspot area is computed, which conforms to contemporary data after rescaling.

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Recovering Joy’s Law as a Function of Solar Cycle, Hemisphere, and Longitude

Cited by 77 publications

References 31 publications

Solar Magnetism in the Polar Regions

Solar Magnetism in the Polar Regions

Evolution of Active Regions

Digitization of sunspot drawings by Spörer made in 1861–1894

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