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Simpson, J. A.

doi:10.1023/a:1005022907102

Cited by 34 publications

(16 citation statements)

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“…ae We consider 26-day variations in the cosmic rays, which are seen up to the highest latitudes observed by Ulysses. This unexpected observation places important constraints on the ability of and the mechanism by which particles are transported in latitude (see also Simpson, 1998). The conclusions of these sections and their implications for our assessment of the global processes which control cosmic ray modulation are summarized in the final section.…”

Section: Introductionmentioning

confidence: 90%

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Fisk

Wenzel

Balogh

et al. 1998

Space Science Reviews

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The global processes that determine cosmic ray modulation are reviewed. The essential elements of the theory which describes cosmic ray behavior in the heliosphere are summarized, and a series of discussions is presented which compare the expectations of this theory with observations of the spatial and temporal behavior of both galactic cosmic rays and the anomalous component; the behavior of cosmic ray electrons and ions; and the 26-day variations in cosmic rays as a function of heliographic latitude. The general conclusion is that the current theory is essentially correct. There is clear evidence, in solar minimum conditions, that the cosmic rays and the anomalous component behave as is expected from theory, with strong effects of gradient and curvature drifts. There is strong evidence of considerable latitude transport of the cosmic rays, at all energies, but the mechanism by which this occurs is unclear. Despite the apparent success of the theory, there is no single choice for the parameters which describe cosmic ray behavior, which can account for all of the observed temporal and spatial variations, spectra, and electron vs. ion behavior.

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Section: Introductionmentioning

confidence: 90%

Untitled

Fisk

Wenzel

Balogh

et al. 1998

Space Science Reviews

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“…Note that such recurrent GCR decreases during HSSs represent the well known 27 day variations (Fonger 1953;Simpson 1998). The intensity then recovered completely or partially, mostly before the trailing edge of the stream.…”

Section: Trains and Recurrent Trains Of Enhanced And Suppressed Diurnmentioning

confidence: 61%

“…Thus corotational variations in solar wind speed are associated with well-known "synodic" or "27 day variations" in the GCR flux (Fonger 1953;Simpson 1998;da Silva et al 2007), which have sometimes been called "recurrent Forbush decreases." An HSS causes a temporary cosmic ray decrease, either due to shielding by the CIR (Heber et al 1999;Richardson 2004) or due to a change in particle diffusion properties in local interplanetary space in low and middle heliolatitudes (Chih & Lee 1986;Kóta & Jokipii 1991).…”

Section: Introductionmentioning

confidence: 99%

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

Yeeram

Ruffolo

Sáiz

et al. 2014

ApJ

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Data from the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand, with a vertical cutoff rigidity of 16.8 GV, were utilized to determine the diurnal anisotropy (DA) of Galactic cosmic rays (GCRs) near Earth during solar minimum conditions between 2007 November and 2010 November. We identified trains of enhanced DA over several days, which often recur after a solar rotation period (∼27 days). By investigating solar coronal holes as identified from synoptic maps and solar wind parameters, we found that the intensity and anisotropy of cosmic rays are associated with the high-speed streams (HSSs) in the solar wind, which are in turn related to the structure and evolution of coronal holes. An enhanced DA was observed after the onset of some, but not all, HSSs. During time periods of recurrent trains, the DA was often enhanced or suppressed according to the sign of the interplanetary magnetic field B, which suggests a contribution from a mechanism involving a southward gradient in the GCR density, n, and a gradient anisotropy along B × ∇n. In one non-recurrent and one recurrent sequence, an HSS from an equatorial coronal hole was merged with that from a trailing mid-latitude extension of a polar coronal hole, and the slanted HSS structure in space with suppressed GCR density can account for the southward GCR gradient. We conclude that the gradient anisotropy is a source of temporary changes in the GCR DA under solar minimum conditions, and that the latitudinal GCR gradient can sometimes be explained by the coronal hole morphology.

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“…The GCR flux depressions appear associated with those periods of time during which the solar wind plasma speed (V ) is >400 km s −1 and/or the IMF intensity (B) is >10 nT (second and fourth panels in Figure 6). This scenario basically corresponds to the passage of high-speed solar wind streams and/or CIRs (Harang 1968;Storini 1990;Cane et al 1995;Simpson 1998;McKibben et al 1999;Bazilevskaya 2000). When GCR short-term variations are correlated with the BV parameter, the role of the magnetic field trend is privileged with respect to that of the solar wind speed as the IMF variations are larger than those of the solar wind speed.…”

Section: Observations Of Gcr Flux Short-term Variations Aboard Lpfmentioning

confidence: 99%

Characteristics and Energy Dependence of Recurrent Galactic Cosmic-Ray Flux Depressions and of a Forbush Decrease with LISA Pathfinder

Armano

Audley

Baird

et al. 2018

ApJ

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Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder, meant for subsystems diagnostics, was devoted to the measurement of GCR and solar energetic particle integral fluxes above 70 MeV n −1 up to 6500 counts s −1 . PD data were gathered with a sampling time of 15 s. Characteristics and energy dependence of GCR flux recurrent depressions and of a Forbush decrease dated 2016 August 2 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections is also discussed.

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Cited by 34 publications

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

Characteristics and Energy Dependence of Recurrent Galactic Cosmic-Ray Flux Depressions and of a Forbush Decrease with LISA Pathfinder

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