The 27-Day Cosmic Ray Intensity Variations During Solar Minimum 23/24

Modzelewska, Renata; Alania, M. V.

doi:10.1007/s11207-013-0261-4

Cited by 39 publications

(39 citation statements)

References 43 publications

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“…2 right panel alongside the solar wind profile where a negative correlation between galactic cosmic ray flux variation and solar wind variation is observed. This is consistent with the negative correlation between solar wind variation and the corresponding galactic cosmic ray variation reported by other authors earlier (Sabbah 2000;Firoz et al 2010;Alania et al 2011;Modzelewska and Alania 2013;Kojima et al 2015). This means that the higher the solar wind the lower the galactic cosmic ray flux and vice-versa.…”

Section: Discussionsupporting

confidence: 92%

“…This is observed to be linearly dependent on solar wind speed which means that the higher the solar wind speed the stronger the modulation parameter thus resulting in a stronger modulation of galactic cosmic ray flux by the solar wind. This thus, result in a negative correlation between galactic cosmic ray flux variation and solar wind speed variation which is in line with earlier report by Gupta et al (2006), Firoz et al (2010, Alania et al (2011), Modzelewska and Alania (2013), Bazilevskaya et al (2013), Tiwari et al (2014), Kojima et al (2015) that galactic cosmic ray intensity variation and solar wind variation are inversely correlated.…”

Section: Discussionsupporting

confidence: 91%

“…The solar wind is known to play a crucial role in controlling the mechanism of transport processes occurring continuously in the heliosphere Alania et al 2011;Modzelewska and Alania 2013). These include convection in the solar wind, diffusion in the heliospheric magnetic field, drift motion due to magnetic field irregularities and adiabatic energy changes (Parker 1965;Sabbah 2000;Aslam and Badruddin 2015).…”

Section: Discussionmentioning

confidence: 99%

“…Among these processes, the solar wind and magnetic field scattering are known to predominantly modulate the flux of galactic cosmic rays (Firoz et al 2010;Alania et al 2011;Modzelewska and Alania 2013). Cliver et al (2013) also asserted that the solar wind is a solar driver of galactic cosmic ray modulation.…”

Section: Introductionmentioning

confidence: 99%

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The effects of solar wind on galactic cosmic ray flux at Earth

Ihongo

Wang

2015

Astrophys Space Sci

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The amount of solar wind produced continuously by the sun is not constant due to changes in solar activity. This unsteady nature of the solar wind seems to be responsible for galactic cosmic ray flux modulation, hence the flux of incoming galactic cosmic rays observed at the top of the Earth's atmosphere varies with the solar wind reflecting the solar activity. The aforementioned reasons have lead to attempts by several researchers to study correlations between galactic cosmic rays and the solar wind. However, most of the correlation studies carried out by authors earlier are based on the analyses of observational data from neutron monitors. In this context, we study the effects of solar wind on galactic cosmic ray flux observed at r ≈ 1 AU, using a theoretical approach and found that the solar wind causes significant decreases in galactic cosmic ray flux at r ≈ 1 AU. A short time variation of the calculated flux is also checked and the result is reflected by exposing a negative correlation of the solar wind with the corresponding galactic cosmic ray flux. This means that the higher the solar wind the lower the galactic cosmic rays flux and vice-versa. To obtain a better understanding, the calculated flux and its short time variation at 1 AU are compared to data that shows a good fit to the model making it possible to establish a statistically significant negative correlation of −0.988 ± 0.001 between solar wind variation and galactic cosmic rays flux variation theoretically.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The effects of solar wind on galactic cosmic ray flux at Earth

Ihongo

Wang

2015

Astrophys Space Sci

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“…They attributed the 27-day variation of GCR intensity to the heliolongitudinal asymmetry of the SW in the inner heliosphere. Modzelewska & Alania (2013) used simulations to show that the product of the SW speed and the strength of the heliospheric magnetic field (HMF) plays an important role in creating the 27-day GCR intensity variation. GCR intensity variation and SW parameters are also known to have a higher correlation during positive minima than during negative minima (Singh & Badruddin 2007;Sabbah 2007).…”

Section: Introductionmentioning

confidence: 99%

Hale cycle and long-term trend in variation of galactic cosmic rays related to solar rotation

Gil

Мурсула

2017

A&A

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Context. Galactic cosmic ray (GCR) intensities around solar minimum times are modulated by magnetic drifts that depend on the overall solar polarity. GCR intensities reach a higher but more narrow peak during negative minima than during positive minima. However, despite these higher intensities, the variation of GCRs over timescales of solar rotation is smaller during negative minima than during positive minima. Aims. We study the variation of GCR intensity over the 27-day synodic solar rotation and over the 14-day half-rotation, in particular the long-term trend and cyclic pattern of this variation, and propose a unifying explanation for the observations. Methods. We used two high-latitude neutron monitors, Oulu and Apatity, which are most sensitive to the low-energy part of the GCR spectrum and thereby more strongly affected by the changes in the conditions of the local heliosphere. We calculated the yearly mean amplitudes of the GCR intensity variation during the full solar rotation (A 27 ) and half-rotation (A 14 ) in 1964-2016. Results. We verify that the A 27 and A 14 amplitudes exhibit a clear 22-yr Hale cycle during solar minima at both stations, with larger amplitudes in positive minima. We find that the mean amplitude of the Hale cycle is about 30-45% of the mean amplitude for A 14 , while is only about 15-30% for A 27 . We also find that all amplitudes depict a declining long-term trend, which we suggest is due to the weakening of solar polar magnetic fields during the last four solar cycles and the ensuing latitudinal widening of the heliospheric current sheet (HCS) region. An exceptionally wide HCS region during the last solar minimum, when A 14 reached its all-time minimum, is demonstrated by Ulysses probe observations. Conclusions. Our results emphasize the effect of polarity-dependent drift and the properties of the HCS in modulating the variation of GCR intensity during solar rotation in solar minimum times. The second rotation harmonic yields a larger Hale amplitude than the first because it is more probable for the Earth to be outside the HCS only once during the rotation than twice or more, which more strongly reduces A 14 during negative polarity times than A 27 . With the HCS region widening from minimum to minimum, the decrease in A 14 is relatively faster than in A 27 .

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Corotating interaction regions and the 27 day variation of galactic cosmic rays intensity at 1 AU during the cycle 23/24 solar minimum

Guo

Florinski

2014

JGR Space Physics

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The results show that the CIR forward/reverse shock pairs or compression/rarefaction regions play important roles in the transport of GCR particles and directly control the observed 27 day periodic intensity variations. We find that stream interfaces (SIs) in CIRs and the heliospheric current sheet (HCS) are both closely associated with the GCR depression onset, in agreement with the observations at 1 AU. The HCS is more important when its tilt angle becomes small during the declining phase of the solar minimum, while the passages of SIs control the onset of GCR depressions for larger HCS tilt angles. The mechanism of GCR intensity variation near 1 AU can be explained through an interplay between the effects of particle drift and diffusion. The simulated plasma background and GCR intensity are compared with the observations from spacecraft and a neutron monitor on the ground, to find good qualitative agreement. Evidently, CIRs had a substantial modulational effect on GCR during the recent solar minimum.

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The 27-Day Cosmic Ray Intensity Variations During Solar Minimum 23/24

Cited by 39 publications

References 43 publications

The effects of solar wind on galactic cosmic ray flux at Earth

The effects of solar wind on galactic cosmic ray flux at Earth

Hale cycle and long-term trend in variation of galactic cosmic rays related to solar rotation

Corotating interaction regions and the 27 day variation of galactic cosmic rays intensity at 1 AU during the cycle 23/24 solar minimum

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