Cyclic variations of the heliospheric tilt angle and cosmic ray modulation

Alanko-Huotari, K.; Usoskin, Ilya; Мурсула, К.; Kovaltsov, Gennady A.

doi:10.1016/j.asr.2007.02.007

Cited by 23 publications

(26 citation statements)

References 27 publications

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“…Parker, 1965;Jokipii, Levy, and Hubbard, 1977). OSF is also included in a model by Alanko-Huotari et al (2007), who found it to be strongly anti-correlated with neutron count rates (e.g. Lockwood, 2003;Rouillard and Lockwood, 2004).…”

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%

“…A model proposed by Alanko-Huotari et al (2007) suggested that the modulation can be described by a combination of the HCS tilt angle, the Suns polarity and the unsigned open solar flux (OSF). This model gives good agreement throughout solar cycles 19-23.…”

Section: Introductionmentioning

confidence: 99%

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

2013

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“…1). However, although the latter varies significantly from cycle to cycle (as reflected in different cycle magnitudes varying by a factor of 2), the tilt angle exhibits roughly the same variations over all cycles, in accord with the idea of a regular cyclic behaviour (Suess et al 1993;Cliver & Ling 2001;Alanko-Huotari et al 2007), depending only on the solar cycle phase and not on its strength. This makes it possible to reconstruct the tilt angle variability using only the solar cycle phase.…”

Section: Reconstruction Of the Hcs Tilt Anglementioning

confidence: 53%

“…Also, the radial model computes results with a higher source surface radius, and accordingly, the current sheet appears flatter and has a lower maximum extent. Here we use the values defined by the radial model, similar to Alanko-Huotari et al (2007), in view of its more robust definition (Wang & Sheeley 1992). Averages of the values produced by WSO over a calendar year are derived and considered as annual values.…”

Section: Reconstruction Of the Hcs Tilt Anglementioning

confidence: 99%

“…Cliver & Ling (2001) concluded, from a similar analysis, that the descending phase of the tilt angle cycle is more gradual for odd cycles, but that is not observed in Figure 2, and moreover the statistic is too low (only two odd cycles) to substantiate such a conclusion. Alanko-Huotari et al (2007) developed an empirical relation describing the cyclic behaviour of the tilt angle for the period 1976-2005. With the WSO tilt angle calculations extending until present, we revisited the model and fitted new parameters.…”

Section: Reconstruction Of the Hcs Tilt Anglementioning

confidence: 99%

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An empirical model of heliospheric cosmic ray modulation on long-term time scale

Asvestari

Usoskin

2016

J. Space Weather Space Clim.

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Galactic Cosmic Rays (GCRs) entering the heliosphere are subject to modulation processes due to variable solar magnetic activity. Finding a relationship between cosmic-ray variations and the heliospheric parameters is important for reconstruction of solar activity in the past. Here, we develop a semi-empirical model describing the heliospheric modulation of GCRs in terms of heliospheric parameters such as the open solar magnetic flux, the tilt angle of the heliospheric current sheet and the polarity of the large scale solar magnetic field. Our model is fitted using annual data obtained for the period 1976-2013, which includes the very weak solar minimum during [2008][2009][2010]. The model shows a good agreement with the data, and therefore, can be used for reconstructions of the modulation potential at different levels of solar activity. The model's validity is also tested using the cosmogenic radionuclides 14 C and 10 Be stored in terrestrial archives. The tilt angle used to fit the parameters in our semi-empirical modulation model is reconstructed by a mathematical model described here.

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Periodicity analysis of galactic cosmic rays using Fourier, Hilbert, and higher-order spectral methods

Vipindas

Gopinath

Girish

2016

Astrophys Space Sci

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Cyclic variations of the heliospheric tilt angle and cosmic ray modulation

Cited by 23 publications

References 27 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

An empirical model of heliospheric cosmic ray modulation on long-term time scale

Periodicity analysis of galactic cosmic rays using Fourier, Hilbert, and higher-order spectral methods

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