The Solar Cycle

Hathaway, David H.

doi:10.1007/lrsp-2010-1

Cited by 106 publications

(80 citation statements)

References 105 publications

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“…Furthermore, polarity reversals do not occur simultaneously at both poles but are often separated by over a year (Babcock, 1959). The present study used polarity reversal times for solar cycles 21-23 from Svalgaard, Cliver, and Kamide (2005) and Hathaway (2012), an extension to the polarity reversal of solar cycle 24 (see Lockwood et al, 2012) and analysis from Babcock (1959) for solar cycle 20.…”

Section: The 22-year Solar Cycle Variationsmentioning

confidence: 99%

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The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

2013

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The ability to predict times of greater galactic cosmic ray (GCR) fluxes is important for reducing the hazards caused by these particles to satellite communications, aviation, or astronauts. The 11-year solar cycle variation in cosmic rays is highly correlated with the strength of the heliospheric magnetic field. Differences in GCR flux during alternate solar cycles yield a 22-year cycle, known as the Hale Cycle, which is thought to be due to different particle drift patterns when the northern solar pole has predominantly positive (denoted a qA>0 cycle) or negative (qA<0) polarities. This results in the onset of the peak cosmic ray flux at Earth occurring earlier during qA>0 cycles than for qA<0 cycles and hence the peak being more domed for qA>0 and more sharply peaked for qA<0. In this study, we demonstrate that properties of the large-scale heliospheric magnetic field are different during the declining phase of the qA<0 and qA>0 solar cycles, when the difference in GCR flux is most apparent. This suggests that particle drifts may not be the sole mechanism responsible for the Hale Cycle in GCR flux at Earth. However, it is also demonstrated that these polarity-dependent heliospheric differences are evident during the space-age but much less clear in earlier data: using geomagnetic reconstructions, it is shown that for the period of 1905 -1965, alternate polarities do not give as significant a difference during the declining phase of the solar cycle. Thus we suggest that the 22-year cycle in cosmic ray flux is at least partly the result of direct modulation by the heliospheric magnetic field and that this effect may be primarily limited to the grand solar maximum of the space-age.

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Section: The 22-year Solar Cycle Variationsmentioning

confidence: 99%

“…The black crosses in figure 1 are times when the average north minus average south polar fields cross zero (this data however is unavailable prior to cycle 20 and so these crosses are not included in Figure 1) This is generally used as a measure of the global solar dipole having reversed (e.g. Hathaway, 2012).…”

Section: The 22-year Solar Cycle Variationsmentioning

confidence: 99%

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

2013

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“…It is traced with several quantities, including the number and area of sunspots (Hoyt & Schatten 1996;Hathaway et al 2002;Usoskin 2008;Hathaway 2010). The cyclic variation of umbral properties such as intensity and magnetic field strength was subject of several investigations (Livingston 2002;Penn & Livingston 2006;Penn & MacDonald 2007;Penn & Livingston 2011;Livingston et al 2012;Pevtsov et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Properties of sunspot umbrae observed in cycle 24

Kiess

Rezaei

Schmidt

2014

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Aims. There is an ongoing debate whether the solar activity cycle is overlaid with a long-term decline that may lead to another grand minimum in the near future. We used the size, intensity, and magnetic field strength of sunspot umbrae to compare the present cycle 24 with the previous one. Methods. We used data of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and selected all sunspots between May 2010 and October 2012, using one image per day. We created two subsets of this dataset with a manual tracking algorithm, both without duplication. One contains each sunspot (910 umbrae within 488 spots) and was used to analyze the distribution of umbral areas, selected with an automated thresholding method. The other subset contains 205 fully evolved sunspots. We estimated their magnetic field and the total magnetic flux and discuss the relations between umbral size, minimum continuum intensity, maximum field strength, and total magnetic flux. Results. We find non-linear relations between umbral minimum intensity and size and between maximum magnetic field strength and size. The field strength scales linearly with the intensity and the umbral size scales roughly linearly with the total magnetic flux, while the size and field strength level off with stronger flux. When separated into hemispheres and averaged temporally, the southern umbrae show a temporal increase in size and the northern umbrae remain constant. We detected no temporal variation in the umbral mean intensity. The probability density function of the umbral area in the ascending phase of the current solar cycle is similar to that of the last solar cycle. Conclusions. From our investigation of umbral area, magnetic field, magnetic flux, and umbral intensity of the sunspots of the rising phase of cycle 24, we do not find a significant difference to the previous cycle, and hence no indication for a long-term decline of solar activity.

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“…The 2 year signals observed in other solar activity proxies are only detectible during phases of moderate to high activity (see, e.g. Vecchio & Carbone 2008;Hathaway 2010, and was also visible in the high-frequency modes during the recent extended minimum may also, therefore, point to behavioural changes in the main dynamo and its influence on the 2-year signal. We are currently exploring the latitudinal dependence of the two-year signal.…”

Section: Evidence For Shorter-term Variations In Solar P-mode Frequenmentioning

confidence: 98%

Helioseismology - a clear view of the interior

2011

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Abstract. Helioseismology is a very powerful tool that allows us to explore the interior of the Sun. Here we give particular emphasis to the justification for the likely location of the zone that is most sensitive to cycle-related changes. For the low degree modes we find that more than one timescale for changes in the oscillations is discovered. We also note the successive cycles have differing sensitivities to the activity. We end with a warning of the risk of being misled with short datasets such as are seen with stellar data.

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The Solar Cycle

Cited by 106 publications

References 105 publications

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

Properties of sunspot umbrae observed in cycle 24

Helioseismology - a clear view of the interior

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