The crucial role of surface magnetic fields for the solar dynamo

Cameron, R. H.; Schüßler, M.

doi:10.1126/science.1261470

Cited by 145 publications

(111 citation statements)

References 19 publications

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“…If the weakness of Cycle 24 continues in the declining phase, only weak poleward surges may result and hence a weaker Cycle 25 is expected. These inferences are based on the expectation from the BabcockLeighton model of solar cycles in that the polar field strength of one cycle determines the phase and amplitude of the next cycle (Babcock 1961;Leighton 1964;Wang & Sheeley 2009;Muñoz-Jaramillo et al 2013;Cameron & Schüssler 2015;Jiang et al 2015). Note that we are mainly talking about the cycle onset, while the precursor method usually predicts the maximum sunspot number in the next cycle and its epoch (Hathaway 2015 and references therein).…”

Section: Discussionmentioning

confidence: 99%

Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25

Gopalswamy

Yashiro

Akiyama

2016

ApJL

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We report on the prolonged solar-maximum conditions until late 2015 at the north-polar region of the Sun indicated by the occurrence of high-latitude prominence eruptions (PEs) and microwave brightness temperature close to the quiet-Sun level. These two aspects of solar activity indicate that the polarity reversal was completed by mid-2014 in the south and late 2015 in the north. The microwave brightness in the south-polar region has increased to a level exceeding the level of the Cycle 23/24 minimum, but just started to increase in the north. The northsouth asymmetry in the polarity reversal has switched from that in Cycle 23. These observations lead us to the hypothesis that the onset of Cycle 25 in the northern hemisphere is likely to be delayed with respect to that in the southern hemisphere. We find that the unusual condition in the north is a direct consequence of the arrival of poleward surges of opposite polarity from the active region belt. We also find that multiple rush-to-the-pole episodes were indicated by the PE locations that lined up at the boundary between opposite-polarity surges. The high-latitude PEs occurred in the boundary between the incumbent polar flux and the insurgent flux of opposite polarity.

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Section: Discussionmentioning

confidence: 99%

Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25

Gopalswamy

Yashiro

Akiyama

2016

ApJL

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“…Cosmic ray variability was calculated in terms of the heliospheric modulation potential (see definitions and formalism in Usoskin et al 2005), also considering α-particles and heavier species of cosmic rays (Webber & Higbie 2009). This modulation potential was furthermore converted into decadal (solar-cycle averaged) sunspot number through the open solar magnetic flux model (Solanki et al 2000;Krivova et al 2007), which relates the solar surface magnetic cycle to the emerging magnetic flux (Cameron & Schüssler 2015). We note that the overall reconstruction method used here is similar to that previously used by Usoskin et al (2014).…”

Section: Reconstructing the Solar Activitymentioning

confidence: 99%

Solar activity during the Holocene: the Hallstatt cycle and its consequence for grand minima and maxima

Usoskin

Gallet

Lopes

et al. 2016

A&A

136

183

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Aims. Cosmogenic isotopes provide the only quantitative proxy for analyzing the long-term solar variability over a centennial timescale. While essential progress has been achieved in both measurements and modeling of the cosmogenic proxy, uncertainties still remain in the determination of the geomagnetic dipole moment evolution. Here we aim at improving the reconstruction of solar activity over the past nine millennia using a multi-proxy approach. Methods. We used records of the 14 C and 10 Be cosmogenic isotopes, current numerical models of the isotope production and transport in Earth's atmosphere, and available geomagnetic field reconstructions, including a new reconstruction relying on an updated archeo-and paleointensity database. The obtained series were analyzed using the singular spectrum analysis (SSA) method to study the millennial-scale trends. Results. A new reconstruction of the geomagnetic dipole field moment, referred to as GMAG.9k, is built for the last nine millennia. New reconstructions of solar activity covering the last nine millennia, quantified in terms of sunspot numbers, are presented and analyzed. A conservative list of grand minima and maxima is also provided. Conclusions. The primary components of the reconstructed solar activity, as determined using the SSA method, are different for the series that are based on 14 C and 10 Be. This shows that these primary components can only be ascribed to long-term changes in the terrestrial system and not to the Sun. These components have therefore been removed from the reconstructed series. In contrast, the secondary SSA components of the reconstructed solar activity are found to be dominated by a common ≈2400-year quasi-periodicity, the so-called Hallstatt cycle, in both the 14 C and 10 Be based series. This Hallstatt cycle thus appears to be related to solar activity. Finally, we show that the grand minima and maxima occurred intermittently over the studied period, with clustering near lows and highs of the Hallstatt cycle, respectively.

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“…Essentially, we refer to a few properties of the Babcock-Leighton phenomenological model. In choosing that model we base ourselves also on Muñoz-Jaramillo et al (2013a, 2013b, Cameron and Schüssler (2015) and Petrie (2015) who find that this model well covers the observational data.…”

Section: The Tachocline; the Origin Of Sunspotsmentioning

confidence: 99%

A Remarkable Recent Transition in the Solar Dynamo

et al. 2016

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We summarize the major aspects of the remarkable, fairly long lasting period (∼ 2005 to ∼ 2010) of low solar activity, that we will call the Transition. It is the transitional stage between the Grand Maximum of the 20th century and a forthcoming (most probably Regular) episode of solar activity. The various kinds of activity in the functioning of the equatorial components of the solar dynamo before and during the Transition are summarized. While the behavior of unipolar magnetic regions and their rest-latitudes already gave very early indications -mid 20th century -of the forthcoming Transition, more such indications became available around 1995 and the main part of it occurred between 2005 and 2010. Some of the inferences are discussed. We submit the hypothesis that the solar tachocline undergoes pulsations and we present some helioseismic evidences. In that scenario we find that its equatorial part has moved downward over a fairly small semi-amplitude (∼ 0.03 solar radii) during the time of the Transition. There are several indications, apart from this 'pulsation', that the tachocline may even be pulsating with still smaller amplitudes in more modes. We speculate about the physical mechanism(s).

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The crucial role of surface magnetic fields for the solar dynamo

Cited by 145 publications

References 19 publications

Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25

Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25

Solar activity during the Holocene: the Hallstatt cycle and its consequence for grand minima and maxima

A Remarkable Recent Transition in the Solar Dynamo

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