Study of the Diurnal Variation of Cosmic Rays during Different Phases of Solar Activity

Tiwari, Anil Kumar; Singh, Ambika; Agrawal, S. P.

doi:10.1007/s11207-012-9962-3

Cited by 17 publications

(15 citation statements)

References 19 publications

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“…It is observed that the annual diurnal amplitude varies according to the 11-year SC, while there is not a similar behavior for the diurnal phase, which is supposed to vary within a period of 22 years (one magnetic SC). This is consistent with the results of Bieber and Chen (1991), Singh and Badruddin (2006), Kudela et al (2008a), Mishra and Mishra (2008), Tiwari et al (2012), and Tezari and Mavromichalaki (2016).…”

Section: Diurnal Anisotropy During the Solar Cyclesupporting

confidence: 92%

“…Athens shows the largest phase variation, as it has the highest threshold rigidity (Bieber and Chen, 1991). It is also observed that there is no significant phase shift during the descending phase of SC 23 and it remains invariant during the ascending phase of SC 24, which is in agreement with the "odd-even" SC model proposed by Tiwari et al (2012).…”

Section: Diurnal Anisotropy During the Solar Cyclesupporting

confidence: 84%

“…On the other hand, the diurnal phase does not seem to present an analogous behavior that is possibly extended to the 22-year magnetic cycle (Bieber and Chen, 1991;Tiwari et al, 2012). …”

Section: Discussionmentioning

confidence: 92%

“…The diurnal amplitude follows the 11-year variation in the solar cycle (SC) (Bieber and Chen, 1991;Tiwari et al, 2012), while the diurnal phase probably displays a correlation with the magnetic solar cycle (22-year variation). This is due to the reversal of the solar magnetic field (SMF) around solar maximum activity (Ahluwalia, 1988).…”

Section: Introductionmentioning

confidence: 90%

“…Then, the annual average diurnal amplitude increases again during the ascending phase of SC 24. Consequently, the amplitude of the diurnal anisotropy displays a clear 11-year sunspot cycle variation, with minima occurring on or near sunspot minimum and maxima near sunspot maximums (Bieber and Chen, 1991;Tiwari et al, 2005Tiwari et al, , 2012Sabbah, 2013). A small increase in diurnal amplitude is observed during 2005, due to various events, such as coronal mass ejections (CMEs) and magnetic storms.…”

Section: Diurnal Anisotropy During the Solar Cyclementioning

confidence: 99%

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Latitudinal and longitudinal dependence of the cosmic ray diurnal anisotropy during 2001–2014

et al. 2016

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Abstract. The diurnal anisotropy of cosmic ray intensity for the time period 2001 to 2014 is studied, covering the maximum and the descending phase of solar cycle 23, the minimum between solar cycles 23 and 24, and the ascending phase and maximum of solar cycle 24. Cosmic ray intensity data from 11 neutron monitor stations located at different places around the Northern Hemisphere obtained from the high-resolution Neutron Monitor Database (NMDB) were used. Special software was developed for the calculations of the amplitude and the phase of the diurnal anisotropy vectors on annual and monthly basis using Fourier analysis and for the creation of the harmonic dial diagrams. The geomagnetic bending for each station was taken into account in our calculations determined from the asymptotic cones of each station via the Tsyganenko96 (Tsyganenko and Stern, 1996) magnetospheric model. From our analysis, it was resulted that there is a different behavior of the diurnal anisotropy vectors during the different phases of the solar cycles depending on the solar magnetic field polarity. The latitudinal and longitudinal distribution of the cosmic ray diurnal anisotropy was also examined by grouping the stations according to their geographic coordinates, and it was shown that diurnal variation is modulated not only by the latitude but also by the longitude of the stations. The diurnal anisotropy during strong events of solar and/or cosmic ray activity is discussed.

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Section: Diurnal Anisotropy During the Solar Cyclesupporting

confidence: 92%

Section: Diurnal Anisotropy During the Solar Cyclesupporting

confidence: 84%

“…On the other hand, the diurnal phase does not seem to present an analogous behavior that is possibly extended to the 22-year magnetic cycle (Bieber and Chen, 1991;Tiwari et al, 2012). …”

Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 90%

Section: Diurnal Anisotropy During the Solar Cyclementioning

confidence: 99%

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Latitudinal and longitudinal dependence of the cosmic ray diurnal anisotropy during 2001–2014

et al. 2016

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Cosmic ray heliospheric transport study with neutron monitor data

et al. 2015

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Determining transport coefficients for galactic cosmic ray (GCR) propagation in the turbulent interplanetary magnetic field (IMF) poses a fundamental challenge in modeling cosmic ray modulation processes. GCR scattering in the solar wind involves wave‐particle interaction, the waves being Alfven waves which propagate along the ambient field (B). Empirical values at 1 AU are determined for the components of the diffusion tensor for GCR propagation in the heliosphere using neutron monitor (NM) data. At high rigidities, particle density gradients and mean free paths at 1 AU in B can only be computed from the solar diurnal anisotropy (SDA) represented by a vector A (components Ar, Aϕ, and Aθ) in a heliospherical polar coordinate system. Long‐term changes in SDA components of NMs (with long track record and the median rigidity of response Rm ~ 20 GV) are used to compute yearly values of the transport coefficients for 1963–2013. We confirm the previously reported result that the product of the parallel (to B) mean free path (λ||) and radial density gradient (Gr) computed from NM data exhibits a weak Schwabe cycle (11y) but strong Hale magnetic cycle (22y) dependence. Its value is most depressed in solar activity minima for positive (p) polarity intervals (solar magnetic field in the Northern Hemisphere points outward from the Sun) when GCRs drift from the polar regions toward the helioequatorial plane and out along the heliospheric current sheet (HCS), setting up a symmetric gradient Gθs pointing away from HCS. Gr drives all SDA components and λ|| Gr contributes to the diffusive component (Ad) of the ecliptic plane anisotropy (A). GCR transport is commonly discussed in terms of an isotropic hard sphere scattering (also known as billiard‐ball scattering) in the solar wind plasma. We use it with a flat HCS model and the Ahluwalia‐Dorman master equations to compute the coefficients α (=λ⊥/λ∥) and ωτ (a measure of turbulence in the solar wind) and transport parameters λ||, λ⊥, Gr, Gθs, and an asymmetric gradient Gθa normal to the ecliptic plane. We study their dependence on rigidity (R), p/n intervals, sunspot numbers (SSNs), and solar wind parameters at 1 AU. λ|| exhibits a strong 22y dependence but Gr does not, explaining solar polarity dependence of λ|| Gr. The computed Gr values are an order of magnitude greater than those reported by our colleagues making an ad hoc assumption that α is low (0.01). At high rigidities, the drift contribution at 1 AU is small and unsteady. A new methodology is outlined to compute yearly GCR north‐south anisotropy (Aθ) from the data for a single detector sorted for p/n intervals. We show that Gθa is the main contributor to Aθ in the steady state, and Gθa is shown not correlated with the north‐south excess SSNs.

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Solar magnetic polarity dependency of the cosmic ray diurnal variation

Sabbah

2013

JGR Space Physics

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[1] Cosmic rays (CRs) data observed through four neutron monitors and one muon telescope are used to study the solar diurnal variation (DV) from 1953 to 2010. The median primary rigidity of response, (R m ), for these detectors encompasses the range 16 ≤ R m ≤ 60 GV of the galactic CRs spectrum. The phase angle observed with the lower rigidity station depends strongly on the solar magnetic field polarity reversal due to drift effect. However, the higher rigidity stations show an 11 year cycle. This cycle is evident in the shape of the cross-correlation functions (CCFs) between the phase angle and the interplanetary magnetic field (IMF) parameters due to diffusion of galactic CRs by the IMF. The amplitude of the DV, IMF magnitude, and solar activity are larger, and the phase angle is later in hours for qA < 0 than for qA > 0. In addition, the amplitude is well correlated with the IMF magnitude. The amplitudes observed by the lower rigidity station peaks 2 years after the IMF magnitude reach maximum for qA < 0. The diurnal amplitude reaches minimum 2-3 years after the solar wind speed peak due to outward convection by solar wind along the helioequator. The phase angle of the higher rigidity station shifts toward the earliest hours, 2 years after the wind speed peaks for qA > 0. This shift is due to outward convection by solar wind that increases the radial component of the DV more than the East-West component.

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Study of the Diurnal Variation of Cosmic Rays during Different Phases of Solar Activity

Cited by 17 publications

References 19 publications

Latitudinal and longitudinal dependence of the cosmic ray diurnal anisotropy during 2001–2014

Latitudinal and longitudinal dependence of the cosmic ray diurnal anisotropy during 2001–2014

Cosmic ray heliospheric transport study with neutron monitor data

Solar magnetic polarity dependency of the cosmic ray diurnal variation

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