Diurnal anisotropy of cosmic rays during intensive solar activity for the period 2001–2014

Tezari, Anastasia; Mavromichalaki, H.

doi:10.1016/j.newast.2015.12.008

Cited by 11 publications

(13 citation statements)

References 23 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%

“…The calculated diurnal vectors of the cosmic ray intensity according to Eqs. (1), (2), (3), and (4) for the selected stations are presented on a harmonic dial on a yearly and monthly basis (Mavromichalaki, 1989;Tezari and Mavromichalaki, 2016;Mavromichalaki et al, 2016) using simple vector calculus and the newly developed DIAS software. The length of the vector represents the diurnal amplitude, while the vector's direction is equivalent to the time of maximum.…”

Section: Discussionmentioning

confidence: 99%

“…During the years 2010-2014 we observe a decreasing cosmic ray intensity corresponding to the minimaximum of solar cycle 24 with a lower value in the solar maximum of this cycle during the years 2012 and 2014 (Aslam and Badruddin, 2015). The years 2003 and 2005 are distinguished from the others due to their strong solar and CR events (Tezari and Mavromichalaki, 2016), even though the applied filters eliminate specific days. Days without events exhibiting intense activity below the filter threshold are clearly still included in the analysis.…”

Section: Diurnal Anisotropy During the Solar Cyclementioning

confidence: 99%

“…Such phenomena include groundlevel enhancements (GLEs), Forbush decreases (FDs) and magnetospheric effects (MEs), which are not interpreted in the same way by every NM (Burlaga and Ness, 1998;Plainaki et al, 2007Plainaki et al, , 2014. The characteristics of diurnal anisotropy show a remarkable variation during these extreme events (Tezari and Mavromichalaki, 2016).…”

Section: Introductionmentioning

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: Discussionmentioning

confidence: 99%

Section: Diurnal Anisotropy During the Solar Cyclementioning

confidence: 99%

Section: Introductionmentioning

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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“…This is primarily observed in NM data during the recovery phase of Forbush decreases caused by coronal mass ejections (e.g. Tezari and Mavromichalaki, 2016) and are named DV "trains". These DV trains can cause DV amplitudes of up to 5 % which can be out of phase with the background DV, as they are caused by the modulating capability of solar wind transients.…”

Section: Introductionmentioning

confidence: 96%

Decadal trends in the diurnal variation of galactic cosmic rays observed using neutron monitor data

et al. 2017

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Abstract. The diurnal variation (DV) in galactic cosmic ray (GCR) flux is a widely observed phenomenon in neutron monitor data. The background variation considered primarily in this study is due to the balance between the convection of energetic particles away from the Sun and the inward diffusion of energetic particles along magnetic field lines. However, there are also times of enhanced DV following geomagnetic disturbances caused by coronal mass ejections or corotating interaction regions. In this study we investigate changes in the DV over four solar cycles using ground-based neutron monitors at different magnetic latitudes and longitudes at Earth. We divide all of the hourly neutron monitor data into magnetic polarity cycles to investigate cycleto-cycle variations in the phase and amplitude of the DV. The results show, in general, a similarity between each of the A < 0 cycles and A > 0 cycles, but with a phase change between the two. To investigate this further, we split the neutron monitor data by solar magnetic polarity between times when the dominant polarity was either directed outward (positive) or inward (negative) at the northern solar pole. We find that the maxima and minima of the DV changes by, typically, 1-2 h between the two polarity states for all non-polar neutron monitors. This difference between cycles becomes even larger in amplitude and phase with the removal of periods with enhanced DV caused by solar wind transients. The time difference between polarity cycles is found to vary in a 22-year cycle for both the maximum and minimum times of the DV. The times of the maximum and minimum in the DV do not always vary in the same manner between A > 0 and A < 0 polarity cycles, suggesting a slight change in the anisotropy vector of GCRs arriving at Earth between polarity cycles. Polar neutron monitors show differences in phase between polarity cycles which have asymptotic directions at mid-to-high latitudes. All neutron monitors show changes in the amplitude of the DV with solar polarity, with the amplitude of the DV being a factor of 2 greater in A < 0 cycles than A > 0 cycles. In most cases the change in timing of the maximum /minimum is greatest with the stations' geomagnetic cut-off rigidity shows little variation in the DV phase with latitude. We conclude that the change in the DV with the dominant solar polar polarity is not as simple as a phase change, but rather an asymmetric variation which is sensitive to the neutron monitor's asymptotic viewing direction.

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The Empirical Implication of Conducting a Chree Analysis Using Data from Isolated Neutron Monitors

Okike

Umahi

2019

Sol Phys

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Diurnal anisotropy of cosmic rays during intensive solar activity for the period 2001–2014

Cited by 11 publications

References 23 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

Decadal trends in the diurnal variation of galactic cosmic rays observed using neutron monitor data

The Empirical Implication of Conducting a Chree Analysis Using Data from Isolated Neutron Monitors

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