New Evidence for Charge-Sign-Dependent Modulation During the Solar Minimum of 2006 to 2009

Felice, V. Di; Munini, R.; Vos, E. E.; Potgieter, M. S.

doi:10.3847/1538-4357/834/1/89

Cited by 31 publications

(21 citation statements)

References 53 publications

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“…This has been done elaborately for protons and electrons. The observed different behaviour between protons and electrons for the mentioned solar minimum period was extensively reported also by [15]. However, this type of study has not yet been done extensively for positrons, and is the focus of this current work.…”

Section: Introductionsupporting

confidence: 60%

Solar modulation of cosmic ray positrons in a very quiet heliosphere

Potgieter¹,

Vos²,

Bisschoff³

et al. 2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

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Since the beginning of the space exploration era, solar activity was observed at its lowest level during 2006 to 2009. During this period, the PAMELA space experiment observed spectra for galactic cosmic rays, specifically for protons, electrons and positrons over a wide energy range, during what is called an A < 0 solar magnetic polarity cycle. Drift theory predicts a difference in the behaviour for these oppositely charge particles during A < 0 cycles. An opportunity was thus created to study the predicted charge-sign-dependent modulation, also now for very quiet heliospheric conditions. A comprehensive three-dimensional, drift modulation model has been used to study the solar modulation for cosmic rays in detail with extensive comparison to the observed PAMELA spectra for the mentioned period. First, this was done for protons and secondly for electrons, as already published, to test and to authenticate the modelling approach and then to come to a better understanding and appreciation of the underlying physics, such as diffusion and drift theory. The results were also used to make predictions of how cosmic rays are differently modulated down to low energies (1 MeV) for the two magnetic polarity cycles of the Sun, and what role drifts play in this process. All computed solutions are based on new very local interstellar spectra, now also done for positrons. This report is focussed on detailed aspects of the solar modulation of positrons during the extraordinary quiet solar modulation period from 2006 to 2009. For the first time, a meaningful modulation factor in the heliosphere is computed for positrons, from 50 GeV down to 1 MeV, as well as the electron to positron ratios as a function of time and rigidity for the mentioned period.

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Section: Introductionsupporting

confidence: 60%

Solar modulation of cosmic ray positrons in a very quiet heliosphere

Potgieter¹,

Vos²,

Bisschoff³

et al. 2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

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show abstract

“…9, the e − /p ratio changes systematically less with time as the rigidity increases. PAMELA observations indicate that during the solar minimum period from 2006 to 2009, charge-sign-dependent effects were not evident (observable) beyond 10-13 GV (Di Felice et al 2017).…”

Section: Electron To Proton Ratiomentioning

confidence: 94%

Difference in the heliospheric modulation of cosmic-ray protons and electrons during the solar minimum period of 2006 to 2009

Potgieter

Vos

2017

A&A

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Context. The PAMELA experiment observed galactic proton and electron spectra down to 70 MV and 400 MV, respectively, from mid-2006 to the end of 2009 during what is called an A < 0 solar magnetic polarity cycle. During this period, solar activity was at its lowest level since the beginning of the space exploration era. This provides the opportunity to study charge-sign-dependent modulation under very quiet heliospheric conditions. Aims. Drift theory for the solar modulation of cosmic rays predicts that the intensity of protons at the Earth is expected to show a different rate of recovery towards solar minimum when compared to electrons during A < 0 cycles. These charge-sign related differences are investigated. Methods. The solutions of a comprehensive three-dimensional drift model are compared to PAMELA spectra to authenticate the modelling approach and then to make predictions of how electrons and protons are differently modulated down to 1 MeV, based on new very local interstellar spectra. Results. The comparison of observations and modelling provides insight into how the rigidity dependence of the three major diffusion coefficients changes during such quiet modulation conditions. How drift effects dissipate above several GeV and below 100 MeV is illustrated for both protons and electrons. The modulation that occurred at the Earth during this quiet period is shown as a function of rigidity and time. The e − /p ratio is computed from 10 MV to 50 GV for this period and a prediction is made for what may be observed in terms of spectra during the next A > 0 solar minimum. Conclusions. The presence of drifts during this quiet period is established based on the presented modelling and PAMELA measurements. Drift effects for protons and electrons are quantified in terms of their rigidity and temporal development from 2006 to 2009.

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“…In this past polarity A < 0 solar minimum, low-energy protons were more sensitive to the changes of heliospheric conditions than low-energy electrons, such phenomenon can be reproduced only by incorporating drifts in the numerical model (Di Felice et al 2017). The PAMELA proton flux data were also used to study the spatial gradients in the inner heliosphere together with proton flux data from Ulysses COSPIN/KET.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Galactic Cosmic Rays in the Inner Heliosphere, Comparing with PAMELA Measurements

Qin

Shen

2017

ApJ

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We develop a numerical model to study the time-dependent modulation of galactic cosmic rays (GCRs) in the inner heliosphere. In the model a time-delayed modified Parker heliospheric magnetic field (HMF) and a new diffusion coefficient model, NLGCE-F, from , are adopted. In addition, the latitudinal dependence of magnetic turbulence magnitude is assumed as ∼ (1 + sin 2 θ)/2 from the observations of Ulysses, and the radial dependence is assumed as ∼ r S , where we choose an expression of S as a function of the heliospheric current sheet (HCS) tilt angle. We show that the analytical expression used to describe the spatial variation of HMF turbulence magnitude agrees well with the Ulysses, Voyager 1, and Voyager 2 observations. By numerically calculating the modulation code we get the proton energy spectra as a function of time during the recent solar minimum, it is shown that the modulation results are consistent with the PAMELA measurements.

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New Evidence for Charge-Sign-Dependent Modulation During the Solar Minimum of 2006 to 2009

Cited by 31 publications

References 53 publications

Solar modulation of cosmic ray positrons in a very quiet heliosphere

Solar modulation of cosmic ray positrons in a very quiet heliosphere

Difference in the heliospheric modulation of cosmic-ray protons and electrons during the solar minimum period of 2006 to 2009

Modulation of Galactic Cosmic Rays in the Inner Heliosphere, Comparing with PAMELA Measurements

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