Peculiarities of cosmic ray modulation in the solar minimum 23/24

Alania, M. V.; Modzelewska, Renata; Wawrzyńczak, A.

doi:10.1002/2013ja019500

Cited by 15 publications

(9 citation statements)

References 37 publications

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“…Mewaldt et al (2010) found ≈ 44 % growth of the parallel mean free path of GCR particles [λ ] from the minimum in 1997 to 2009 and its rapid reduction in 2010. Cliver, Richardson, and Ling (2013) stated that particle drifts were not the main processes in the recent minimum, but the GCR modulation was determined by diffusion and convection, contradicting the results obtained by Alania, Modzelewska, and Wawrzynczak (2014), i.e. that a drift related to the delay time between tilt angles of heliospheric current sheet and cosmic-ray intensity was an important reason for an increase of cosmic-ray intensity in 2009.…”

Section: Introductionmentioning

confidence: 89%

Energy Spectrum of the Recurrent Variation of Galactic Cosmic Rays During the Solar Minimum of Cycles 23/24

Gil

Alania

2016

Sol Phys

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The Sun during the recent epoch of solar activity operated in a different way than during the last 60 years, being less active. We study temporal changes of the energy spectrum of the first three harmonics of the 27-day variation of the galactic cosmic rays (GCR) intensity during the unusual, recent solar minimum, between Solar Cycles 23 and 24 (SC 23/24) and compare with four previous minima. We show that the energy spectrum of the amplitudes of the recurrent variation of the GCR intensity is hard in the maximum epochs and is soft in the minimum epochs during Solar Cycles 20 -24, but with peculiarities during the Solar Minimum 23/24. In particular, while the energy/rigidity spectrum of the amplitudes of the first harmonic of the recurrent variation of the GCR intensity behaves practically the same as for previous epochs, the energy/rigidity spectrum of the amplitudes of the second and the third harmonics demonstrates a pronounced softening. We attribute this phenomenon to the decrease of the extension of the heliosphere caused by the decrease of the solar-wind dynamic pressure during the unusual Solar Minimum 23/24.

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Section: Introductionmentioning

confidence: 89%

Energy Spectrum of the Recurrent Variation of Galactic Cosmic Rays During the Solar Minimum of Cycles 23/24

Gil

Alania

2016

Sol Phys

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“…The UNLT theory was extended to allow for dynamical turbulence in [42]. If we consider particles moving much faster than the Alfvén speed, the static approximation should be accurate and equation (15) becomes in this case…”

Section: The Unlt Theorymentioning

confidence: 99%

“…The knowledge of the diffusion tensor is required in different physical scenarios such as modeling the propagation of cosmic particles in the Galaxy [10,11], studying solar modulation [12][13][14][15][16], and describing particles experiencing diffusive acceleration at interplanetary shocks [17][18][19][20][21] and interstellar shocks [22,23].…”

Section: Introductionmentioning

confidence: 99%

The influence of the Kubo number on the transport of energetic particles

Shalchi

2016

New J. Phys.

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We discuss the interaction between charged energetic particles and magnetized plasmas by using analytical theory. Based on the unified nonlinear transport (UNLT) theory we compute the diffusion coefficient across a large scale magnetic field. To achieve analytical tractability we use a simple Gaussian approach to model the turbulent magnetic fields. We show that the perpendicular diffusion coefficient depends only on two parameters, namely the Kubo number and the parallel mean free path. We combine the aforementioned turbulence model with the UNLT theory and we solve the corresponding integral equation numerically to show how these two parameters control the perpendicular diffusion coefficient. Furthermore, we consider two extreme cases, namely the case of strong and suppressed pitch-angle scattering, respectively. For each case we consider small and large Kubo numbers to achieve a further simplification. All our analytical findings are compared with formulas which are known in diffusion theory.

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“…At lower rigidities, drifts are present at all phases of a sunspot cycle [ Bieber et al, ; Asioka et al, ]. Potgieter et al ' s [] analysis of proton data from PAMELA spacecraft [ Adriani et al, ] confirmed Cliver et al's contention that residual modulation in 2009 is more diffusion like than in previous solar minima but insisting that drifts played a significant role although observed modulation effects are not well correlated with the waviness of the heliospheric current sheet (HCS) as in previous solar minima; also, see discussion by Alania et al [].…”

Section: Introductionmentioning

confidence: 99%

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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Peculiarities of cosmic ray modulation in the solar minimum 23/24

Cited by 15 publications

References 37 publications

Energy Spectrum of the Recurrent Variation of Galactic Cosmic Rays During the Solar Minimum of Cycles 23/24

Energy Spectrum of the Recurrent Variation of Galactic Cosmic Rays During the Solar Minimum of Cycles 23/24

The influence of the Kubo number on the transport of energetic particles

Cosmic ray heliospheric transport study with neutron monitor data

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