Evolution of Coronal Holes and Implications for High-Speed Solar Wind During the Minimum Between Cycles 23 and 24

Toma, G. de

doi:10.1007/s11207-010-9677-2

Cited by 118 publications

(97 citation statements)

References 37 publications

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“…Nevertheless, the time series shown in the two panels of Figure 19 are clearly well correlated with each other, evidence that they represent real patterns in the polar field evolution. They agree, for example, on the widely-reported fact that the polar fields, both north and south, have been only about 60% as strong since the cycle 23 polarity reversal compared to before (e.g., Hoeksema, 2010;de Toma, 2011). Around the time of this reversal of polarity, 2002 -2003, the positive and negative flux latitude centroids began to converge in each hemisphere (Petrie, 2012, see Figure 18).…”

Section: Chromospheric Synoptic Maps and Potential-field Extrapolationssupporting

confidence: 77%

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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: Chromospheric Synoptic Maps and Potential-field Extrapolationssupporting

confidence: 77%

“…This also resulted in a more complex coronal structure with more low-latitude coronal holes during the cycle 23/24 minimum than during the previous minimum (de Toma, 2011). We will discuss this topic further in Section 4.2.…”

Section: Unusual Cycle 23 Minimummentioning

confidence: 99%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

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“…This apparent insensitivity of the GCR flux to the weaker solar wind can be due to a non-dipolar configuration of the corona and heliosphere, which is anomalous in the minimum phase of the solar cycle. This complex heliospheric configuration could explain the unusual solar wind properties recorded at Earth, i.e., in the ecliptic plane (de Toma 2010).…”

Section: Introductionmentioning

confidence: 87%

“…The IMF strength was 30% below past minima (McComas et al 2008;Smith & Balogh 2008;Fisk & Zhao 2009;Heber et al 2009;Cliver & Ling 2010;de Toma et al 2010;Jian et al 2011). This weakening can at least partly be associated with a parallel weakening of the observed polar magnetic field, by 40% (Sheeley 2008;Wang et al 2009;Janardhan et al 2010).…”

Section: Introductionmentioning

confidence: 93%

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Are the sunspots really vanishing?

Clette

Lefèvre

2012

J. Space Weather Space Clim.

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Context:The elapsed solar cycle (23) ended with an exceptionally long period of low activity and with unprecedented low levels for various series of solar irradiance and particle flux measurements. This unpredicted evolution of solar activity raised multiple questions about a future decline of the solar cycles and launched a quest for precursor signs of this possible deep solar transition over the last decade. Aim: We present here a review and overall interpretation of most current diagnostics of solar cycle 23, including the recent disagreements that appeared among solar reference indices and standard solar-based geo-indices, the indication of a changed pattern of internal torsional waves (helioseismology) or the announced fading and magnetic weakening of sunspots. Methods: Based on a statistical analysis of detailed sunspot properties over the last 24 years, we complete the picture with new evidence of a strong global deficit of the smallest sunspots starting around 2000, in order to answer the question: are all sunspots about to disappear? Results: This global scale-dependent change in sunspot properties is confirmed to be real and not due to uncontrolled biases in some of the indices. It can also explain the recent discrepancies between solar indices by their different sensitivities to small and weak magnetic elements (small spots). The International Sunspot Index R i , based on unweighted sunspot counts, proved to be particularly sensitive to this particular small-scale solar evolution. Conclusions: Our results and interpretation show the necessity to look backwards in time, more than 80 years ago. Indeed, the Sun seems to be actually returning to a past and hardly explored activity regime ending before the 1955-1995 Grand Maximum, which probably biased our current space-age view of solar activity.

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Centennial variations in sunspot number, open solar flux and streamer belt width: 3. Modeling

Lockwood

Owens

2014

JGR Space Physics

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From the variation of near-Earth interplanetary conditions, reconstructed for the mid-19 th century to the present day using historic geomagnetic activity observations, Lockwood and Owens (2014) have suggested that Earth remains within a broadened streamer belt during solar cycles when the Open Solar Flux (OSF) is low. From this they propose that the Earth was immersed in almost constant slow solar wind during the Maunder minimum (c. 1650-1710). In this paper, we extend continuity modeling of the OSF to predict the streamer belt width using both group sunspot numbers and corrected international sunspot numbers to quantify the emergence rate of new OSF. The results support the idea that the solar wind at Earth was persistently slow during the Maunder minimum because the streamer belt was broad.

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Evolution of Coronal Holes and Implications for High-Speed Solar Wind During the Minimum Between Cycles 23 and 24

Cited by 118 publications

References 37 publications

Solar Magnetism in the Polar Regions

Solar Magnetism in the Polar Regions

Are the sunspots really vanishing?

Centennial variations in sunspot number, open solar flux and streamer belt width: 3. Modeling

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