Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere

Cummings, A. C.; Stone, E. C.; Webber, W. R.

doi:10.1029/gl014i003p00174

Cited by 85 publications

(55 citation statements)

References 20 publications

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“…The derived radial gradients of 2.8 ± 0.2%/AU for 1.9 GV protons (De Simone et al 2011;Gieseler & Heber 2016) were similar to those found in previous studies (Cummings et al 1987;McKibben 1975;Heber et al 1996). The measured latitudinal gradient was found to be slightly negative, −0.06 ± 0.01%/…”

Section: Outside the Ecliptic Planesupporting

confidence: 79%

Solution of Heliospheric Propagation: Unveiling the Local Interstellar Spectra of Cosmic-ray Species

Boschini

Torre

Gervasi

et al. 2017

ApJ

150

181

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Local interstellar spectra (LIS) for protons, helium and antiprotons are built using the most recent experimental results combined with the state-of-the-art models for propagation in the Galaxy and heliosphere. Two propagation packages, GALPROP and HelMod, are combined to provide a single framework that is run to reproduce direct measurements of cosmic ray (CR) species at different modulation levels and at both polarities of the solar magnetic field. To do so in a self-consistent way, an iterative procedure was developed, where the GALPROP LIS output is fed into HelMod that provides modulated spectra for specific time periods of selected experiments to compare with the data; the HelMod parameters optimization is performed at this stage and looped back to adjust the LIS using the new GALPROP run. The parameters were tuned with the maximum likelihood procedure using an extensive data set of proton spectra from 1997-2015. The proposed LIS accommodate both the low energy interstellar CR spectra measured by Voyager 1 and the high energy observations by BESS, Pamela, AMS-01, and AMS-02 made from the balloons and near-Earth payloads; it also accounts for Ulysses counting rate features measured out of the ecliptic plane. The found solution is in a good agreement with proton, helium, and antiproton data by AMS-02, BESS, and PAMELA in the whole energy range.

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Section: Outside the Ecliptic Planesupporting

confidence: 79%

Solution of Heliospheric Propagation: Unveiling the Local Interstellar Spectra of Cosmic-ray Species

Boschini

Torre

Gervasi

et al. 2017

ApJ

150

181

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“…During 1981-1990 the LMF polarity was negative (A <0) and theories predict that the bi-directional latitudinal gradient should be directed towards the solar equatorial plane. This has been confirmed (Christon et al 1986, Cummings et al 1987, Webber and Lockwood 1992.…”

Section: Latitudinal Density Gradientsupporting

confidence: 58%

Modulation of high‐energy cosmic rays in the heliosphere

Hall¹,

Humble²,

Duldig³

1994

J. Geophys. Res.

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DECLARATIONSI certify that this thesis does not incorporate without acknowledgment any material previously submitted for a degree or diploma in any university; and to the best of my knowledge and belief it does not contain any material previously published or written by another person where due reference is not made in the text. Damian Lindsay Hallll This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968. Damian Lindsay Hall Ill ABSTRACTThe distribution of galactic cosmic ray particles in the heliosphere is influenced (modulated) by the Sun's interplanetary magnetic field (IMF) and the solar wind. The particles diffuse inward, convect outward and have drifts in the motion of their gyro-centres. They are also scattered from their gyro-orbits by irregularities in the IMF. These processes are the components of solar modulation and produce streaming (anisotropies) of particles in the heliosphere. The anisotropies can be investigated at Earth by examining the count rates of cosmic ray detectors. The anisotropic streams appear as diurnal and semi-diurnal variations in the count rates of cosmic ray recorders in solar and sidereal time. Theoretical models of solar modulation predict effects which are dependent on the polarity of the Sun's magnetic dipole (A >0 or A <0). The solar diurnal and North-South anisotropy can be used to test these predictions.The yearly averaged solar and sidereal diurnal variations in data recorded by seven neutron monitors and ten muon telescopes for the period 1957 to 1990 have been deduced by Fourier analysis methods. The rigidities of the galactic cosmic rays to which these instruments respond encompass the range 10 to 1400 Giga volts (GV). The rigidity spectrum of the solar diurnal anisotropy has been inferred to have a mean spectral index extremely close to zero and an idealised upper limiting rigidity of 100± 25 GV. This is in good agreement with previous determinations. It is shown that this upper limit has a temporal variation between 50 GV and 180 GV and is correlated with the magnitude of the IMF. The rigidity spectrum is likely to be dependent on the polarity of the Sun's magnetic dipole, the spectral index being determined as positive in the A >0 magnetic polarity state and negative in the A <0 polarity state. It is also shown that the amplitude of the anisotropy varies with an 11-year variation and the time of maximum varies with 22-year variation. Both of these variations are shown to be independent of any change in the rigidity spectrum.The solar diurnal anisotropy is also used as a tool to calculate the modulation parameters ?Lip, (the product of the parallel mean-free path and radial density gradient) and Gtzl (an indicator of the symmetric latitudinal density gradient). X G r is found to have a 22-year II variation at all rigidities studied and furthermore to only have rigidity dependence when the heliosphere is in the A >0 magnetic polarity state. It is unlikely that X IIG r has any rigidity dependence in the A <0 polarity s...

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“…These models had very specific predictions, for instance, marked differences in the GCR intensity time-profiles in consecutive solar cycles (plateau vs peaked shape in A > 0 and A < 0 cycles for positively charged particles, respectively), as well as differences in the radial and latitudinal gradients of GCRs. These features were confirmed by observations [1,4]. Their magnitude, however, tend to be smaller than prediction obtained by purely drift-dominated models [29].…”

Section: Some Numerical Tools and Approachessupporting

confidence: 76%

On the causes and mechanisms of the long-term variations in the GCR characteristics

Крайнев¹,

Kóta²,

Potgieter³

2016

Proceedings of the 34th International Cosmic Ray Conference — PoS(ICRC2015)

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We argue that the degree of understanding the causes and mechanisms of the long-term variations (11-year and 22-year) in the galactic cosmic rays (GCR) characteristics is still insufficient and to improve it we need new approaches and methods. For the time being there is a long-lasting controversy on how these long-term variations, observed for more than 50 years in the inner heliosphere, are formed. It is widely believed that the 11-year variation is due entirely to the toroidal branch of solar activity (the area and number of sunspots, the strength of the heliospheric magnetic field etc) because of the diffusion, convection and adiabatic energy loss, while the much smaller 22-year variation is caused by the particle drifts connected with the poloidal branch of solar activity (the high-latitude solar magnetic fields). At the same time, both past and more recent numerical simulations indicate that the contribution of particle drifts could be significant for both 22-and 11-year variations in the GCR intensities. However, even those who agree on the significant influence of drifts appear to have different perceptions on the mechanisms of this influence. In this paper, we present an analysis of the possible causes of the first point of view (small role of drifts in the 11-year GCR variation) and the reasons why one can expect the significant contribution of the processes connected with the poloidal branch of solar activity in both types of the long-term variations of the GCR characteristics. Then we briefly discuss some numerical methods suggested in the past and recently and the approaches and perspectives for the sought-for methods are considered.

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Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere

Cited by 85 publications

References 20 publications

Solution of Heliospheric Propagation: Unveiling the Local Interstellar Spectra of Cosmic-ray Species

Solution of Heliospheric Propagation: Unveiling the Local Interstellar Spectra of Cosmic-ray Species

Modulation of high‐energy cosmic rays in the heliosphere

On the causes and mechanisms of the long-term variations in the GCR characteristics

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