Corotating Solar Wind Structures and Recurrent Trains of Enhanced Diurnal Variation in Galactic Cosmic Rays

Yeeram, T.; Ruffolo, D.; Sáiz, A.; Kamyan, N.; Nutaro, Tanin

doi:10.1088/0004-637x/784/2/136

Cited by 18 publications

(10 citation statements)

References 40 publications

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“…The average mass and kinetic energy of coronal mass ejections were around five times lower in comparison with the previous minimum (Vourlidas et al, 2010), diminishing one of the barriers for entrance of GCR particles into the inner heliosphere (Mewaldt, 2013). Zhao et al (2014) also stated that a low magnetic turbulence, increasing the parallel diffusion and reducing the perpendicular diffusion in the polar direction, might be another phenomenon giving rise to the observed higher GCR intensity.…”

Section: Introductionmentioning

confidence: 82%

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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: 82%

“…Moreover, the heliosphere changes over time, and those changes influence the GCR stream on different time scales (e.g. Kudela, 2013;Yeeram et al, 2014). The recurrent variation of the galactic cosmic-ray intensity was described for the (Forbush, 1938) and is still of interest.…”

Section: Introductionmentioning

confidence: 99%

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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“…A neutron monitor is a standard ground-based instrument for measuring time variations in the flux of galactic cosmic rays (GCRs) by detecting secondary particles (mostly neutrons) from their atmospheric showers. Ground-based measurements of GCR flux variations over 22 year solar magnetic cycles, 11 year sunspot cycles, and the Sun's 27 day rotation period, as well as the GCR anisotropy from diurnal count rate variations over the Earth's 1 day rotation period, provide unique and important information about the state of the heliosphere [Okazaki et al, 2008;Yeeram et al, 2014;Nuntiyakul et al, 2014]. Cosmic rays can reach a given location on Earth only if their rigidity (related to momentum per charge) exceeds the local geomagnetic cutoff rigidity.…”

Section: Introductionmentioning

confidence: 99%

Measurement and simulation of neutron monitor count rate dependence on surrounding structure

et al. 2015

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Neutron monitors are the premier instruments for precise measurements of time variations (e.g., of solar origin) in the galactic cosmic ray (GCR) flux in the range of ∼1–100 GeV. However, it has proven challenging to accurately determine the yield function (effective area) versus rigidity in order to relate a neutron monitor's count rate with those of other monitors worldwide and the underlying GCR spectrum. Monte Carlo simulations of the yield function have been developed, but there have been few opportunities to validate these observationally, especially regarding the particular environment surrounding each monitor. Here we have precisely measured the count rate of a calibration neutron monitor near the Princess Sirindhorn Neutron Monitor (PSNM) at Doi Inthanon, Thailand (18.59∘N, 98.49∘E, 2560 m altitude), which provides a basis for comparison with count rates of other neutron monitors worldwide that are similarly calibrated. We directly measured the effect of surrounding structure by operating the calibrator outside and inside the building. Using Monte Carlo simulations, we clarify differences in response of the calibrator and PSNM, as well as the calibrator outside and inside the building. The dependence of the calibrator count rate on surrounding structure can be attributed to its sensitivity to neutrons of 0.5–10 MeV and a shift of sensitivity to nucleons of higher energy when placed inside the building. Simulated calibrator to PSNM count rate ratios inside and outside agree with observations within a few percent, providing useful validation and improving confidence in our ability to model the yield function for a neutron monitor station.

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“…More generally, the anisotropy, which relates to the flow of GCRs in space, has long been known to vary with the ∼11 yr solar activity cycle, and provided the first indication of effects of the ∼22 yr solar magnetic cycle on cosmic rays (Thambyahpillai & Elliot 1953). The GCR flux and anisotropy at ∼1-100 GeV are also known to vary with the 27 day solar rotation period in association with high speed solar wind streams and reversals of the interplanetary magnetic field (Okazaki et al 2008;Yeeram et al 2014;Modzelewska & Alania 2018).…”

Section: Introductionmentioning

confidence: 99%

Extended Cosmic Ray Decreases with Strong Anisotropy after Passage of Interplanetary Shocks

Buatthaisong

Ruffolo

Sáiz

et al. 2022

ApJ

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The passage of an interplanetary shock and/or interplanetary coronal mass ejection often causes a rapid decrease in the Galactic cosmic-ray (GCR) flux, known as a Forbush decrease, followed by a recovery of the flux over some days. These local effects are of short duration and strongly rigidity dependent, with higher-rigidity particles exhibiting much weaker effects. In contrast, we present data for two events in which the cosmic-ray flux gradually decreased for about 1 week after shock passage, then recovering over the following week, with the highest anisotropy levels observed throughout Solar Cycle 24. These extended decreases have a weak rigidity dependence and are much more prominent in observations at higher cutoff rigidity, where the initial Forbush decrease is not clearly detected and other variations are generally weak, as we demonstrate using data from the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand with a cutoff rigidity of about 17 GV. We propose that these extended decrease events were initiated upon the passage of an interplanetary shock that inhibited the inflow of GCRs along the interplanetary magnetic field, possibly due to magnetic mirroring at the shock. We also discuss the general behavior of GCR anisotropy as observed at this high cutoff rigidity.

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Corotating Solar Wind Structures and Recurrent Trains of Enhanced Diurnal Variation in Galactic Cosmic Rays

Cited by 18 publications

References 40 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

Measurement and simulation of neutron monitor count rate dependence on surrounding structure

Extended Cosmic Ray Decreases with Strong Anisotropy after Passage of Interplanetary Shocks

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