Time variations of cosmic ray electrons and nuclei between 1978 and 2004: Evidence for charge‐dependent modulation organized by changes in solar magnetic polarity and current sheet tilt

Webber, W. R.; Heber, B.; Lockwood, J. A.

doi:10.1029/2005ja011291

Cited by 10 publications

(3 citation statements)

References 23 publications

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“…The rigidity P is calculated from the particle momentum p by

P = \frac{pc}{| Z | e}

. It has been shown previously that ions with the same ratio

\frac{Ze}{A}

like helium, carbon, or oxygen undergo the same temporal variation (e.g., Heber et al, ; Gieseler et al, ; McDonald et al, ; Webber et al, ). We take advantage of this and use IMP‐8 helium and ACE/CRIS carbon measurements as proxies for protons at the same rigidity.…”

Section: Observation and Data Analysismentioning

confidence: 99%

An Empirical Modification of the Force Field Approach to Describe the Modulation of Galactic Cosmic Rays Close to Earth in a Broad Range of Rigidities

2017

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On their way through the heliosphere, galactic cosmic rays (GCRs) are modulated by various effects before they can be detected at Earth. This process can be described by the Parker equation, which calculates the phase space distribution of GCRs depending on the main modulation processes: convection, drifts, diffusion, and adiabatic energy changes. A first‐order approximation of this equation is the force field approach, reducing it to a one‐parameter dependency, the solar modulation potential ϕ. Utilizing this approach, it is possible to reconstruct ϕ from ground‐based and spacecraft measurements. However, it has been shown previously that ϕ depends not only on the local interstellar spectrum (LIS) but also on the energy range of interest. We have investigated this energy dependence further, using published proton intensity spectra obtained by PAMELA and heavier nuclei measurements from IMP‐8 and ACE/CRIS. Our results show severe limitations at lower energies including a strong dependence on the solar magnetic epoch. Based on these findings, we will outline a new tool to describe GCR proton spectra in the energy range from a few hundred MeV to tens of GeV over the last solar cycles. In order to show the importance of our modification, we calculate the global production rates of the cosmogenic radionuclide 10Be which is a proxy for the solar activity ranging back thousands of years.

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“…The rigidity P is calculated from the particle momentum p by

P = \frac{pc}{| Z | e}

. It has been shown previously that ions with the same ratio

\frac{Ze}{A}

Section: Observation and Data Analysismentioning

confidence: 99%

An Empirical Modification of the Force Field Approach to Describe the Modulation of Galactic Cosmic Rays Close to Earth in a Broad Range of Rigidities

2017

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“…These drifts have long been known to have significant effects on cosmic-ray transport, and hence on cosmic-ray modulation (e.g Jokipii & Kopriva 1979;Jokipii & Thomas 1981), even in the heliosheath (Kota 2016). Drift effects account for the 22-year cycle observed in cosmic-ray intensities (Jokipii & Thomas 1981), lead to a strong dependence of observed cosmic-ray intensities on the solar tilt angle ) and heliospheric magnetic field polarity (Webber et al 2005), as well as having a significant influence on observed global cosmic-ray modulation phenomena such as observed latitude gradients (Heber et al 1996;Zhang 1997;de Simone et al 2011). Drift effects may even be of importance to the study of solar energetic particles (e.g.…”

Section: Introductionmentioning

confidence: 99%

Toward a Greater Understanding of the Reduction of Drift Coefficients in the Presence of Turbulence

Engelbrecht

Strauss

Roux

et al. 2017

ApJ

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Drift effects play a significant role in the transport of charged particles in the heliosphere. A turbulent magnetic field is also known to reduce the effects of particle drifts. The exact nature of this reduction, however, is not clear. This study aims to provide some insight into this reduction, and proposes a relatively simple, tractable means of modelling it that provides results in reasonable agreement with numerical simulations of the drift coefficient in a turbulent magnetic field.

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“…The coefficient κ A is the drift coefficient and intervenes mostly for very energetic particles and strong gradients of the magnetic field (Jokipii and Levy, 1977). It takes into account the influence of the current sheet (Jokipii and Thomas, 1981), the solar tilt angle (Lockwood and Webber, 2005) and heliospheric magnetic field polarity (Webber et al, 2005). Drift effects also contribute to the 22-year cycle observed in the CR intensity and the CR latitudinal gradients (Heber et al, 1996).…”

Section: Diffusion Coefficientsmentioning

confidence: 99%

Impact of solar magnetic field amplitude and geometry on cosmic rays diffusion coefficients in the inner heliosphere

Perri

Brun

Strugarek

et al. 2020

J. Space Weather Space Clim.

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p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Helvetica} span.s1 {font: 5.5px Helvetica} Cosmic rays are remarkable tracers of solar events when they are associated with solar flares, but also galactic events such as supernova remnants when they come from outside our solar system. Solar Energetic Particles (SEPs) are correlated with the 11-year solar cycle while Galactic Cosmic Rays (GCRs) are anti correlated due to their interaction with the heliospheric magnetic field and the solar wind. Our aim is to quantify separately the impact of the amplitude and the geometry of the magnetic field, both evolving during the solar cycle, on the propagation of cosmic rays of various energies in the inner heliosphere (within Earth orbit). We focus especially on the diffusion caused by the magnetic field along and across the field lines. To do so, we use the results of 3D magnetohydrodynamics (MHD) wind simulations running from the lower corona up to 1 AU. This gives us the structure of the wind and the corresponding magnetic field. The wind is modeled using a polytropic approximation, and fits and power laws are used to account for the turbulence. Using these results, we compute the parallel and perpendicular diffusion coefficients of the Parker cosmic ray transport equation, yielding 3D maps of the diffusion of cosmic rays in the inner heliosphere. By varying the amplitude of the magnetic field, we change the amplitude of the diffusion by the same factor, and the radial gradients by changing the spread of the current sheet. By varying the geometry of the magnetic field, we change the latitudinal gradients of diffusion by changing the position of the current sheets. By varying the energy, we show that the distribution of values for SEPs is more peaked than GCRs. For realistic solar configurations, we show that diffusion is highly non-axisymmetric due to the configuration of the current sheets, and that the distribution varies a lot with the distance to the Sun with a drift of the peak value. This study shows that numerical simulations, combined with theory, can help quantify better the influence of the various magnetic field parameters on the propagation of cosmic rays. This study is a first step towards the resolution of the complete Parker transport equation to generate synthetic cosmic rays rates from numerical simulations.

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Time variations of cosmic ray electrons and nuclei between 1978 and 2004: Evidence for charge‐dependent modulation organized by changes in solar magnetic polarity and current sheet tilt

Cited by 10 publications

References 23 publications

An Empirical Modification of the Force Field Approach to Describe the Modulation of Galactic Cosmic Rays Close to Earth in a Broad Range of Rigidities

An Empirical Modification of the Force Field Approach to Describe the Modulation of Galactic Cosmic Rays Close to Earth in a Broad Range of Rigidities

Toward a Greater Understanding of the Reduction of Drift Coefficients in the Presence of Turbulence

Impact of solar magnetic field amplitude and geometry on cosmic rays diffusion coefficients in the inner heliosphere

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