Radial and latitudinal gradients of anomalous cosmic ray oxygen in the inner heliosphere

Cummings, A. C.; Tranquille, C.; Marsden, R. G.; Mewaldt, R. A.; Stone, E. C.

doi:10.1029/2009gl039851

Cited by 11 publications

(20 citation statements)

References 26 publications

(26 reference statements)

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“…• Anomalous fluxes of oxygen, nitrogen, and neon were observed along the Ulysses trajectory and at Earth and with spatial gradients different from galactic CRs (e.g., Heber and Marsden, 2001;Cummings et al, 2009).…”

Section: Samples From the Inner Heliospherementioning

confidence: 97%

Solar Modulation of Cosmic Rays

Potgieter

2013

Living Rev. Solar Phys.

479

377

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This is an overview of the solar modulation of cosmic rays in the heliosphere. It is a broad topic with numerous intriguing aspects so that a research framework has to be chosen to concentrate on. The review focuses on the basic paradigms and departure points without presenting advanced theoretical or observational details for which there exists a large number of comprehensive reviews. Instead, emphasis is placed on numerical modeling which has played an increasingly significant role as computational resources have become more abundant. A main theme is the progress that has been made over the years. The emphasis is on the global features of CR modulation and on the causes of the observed 11-year and 22-year cycles and charge-sign dependent modulation. Illustrative examples of some of the theoretical and observational milestones are presented, without attempting to review all details or every contribution made in this field of research. Controversial aspects are discussed where appropriate, with accompanying challenges and future prospects. The year 2012 was the centennial celebration of the discovery of cosmic rays so that several general reviews were dedicated to historical aspects so that such developments are briefly presented only in a few cases.

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Section: Samples From the Inner Heliospherementioning

confidence: 97%

Solar Modulation of Cosmic Rays

Potgieter

2013

Living Rev. Solar Phys.

479

377

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“…By separating the variations in radial distance and latitude (Bastian et al 1980;McKibben et al 1979) and approximating them with an exponential function (e.g. Cummings et al 2009), Eq. (2) can be rewritten as…”

Section: Gradient Calculationmentioning

confidence: 99%

Spatial gradients of GCR protons in the inner heliosphere derived fromUlyssesCOSPIN/KET and PAMELA measurements

Gieseler¹,

Heber²

2016

A&A

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Context. During the transition from solar cycle 23 to 24 from 2006 to 2009, the Sun was in an unusual solar minimum with very low activity over a long period. These exceptional conditions included a very low interplanetary magnetic field (IMF) strength and a high tilt angle, which both play an important role in the modulation of galactic cosmic rays (GCR) in the heliosphere. Thus, the radial and latitudinal gradients of GCRs are very much expected to depend not only on the solar magnetic epoch, but also on the overall modulation level. Aims. We determine the non-local radial and the latitudinal gradients of protons in the rigidity range from ∼0.45 to 2 GV. Methods. This was accomplished by using data from the satellite-borne experiment Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) at Earth and the Kiel Electron Telescope (KET) onboard Ulysses on its highly inclined Keplerian orbit around the Sun with the aphelion at Jupiter's orbit. Results. In comparison to the previous A > 0 solar magnetic epoch, we find that the absolute value of the latitudinal gradient is lower at higher and higher at lower rigidities. This energy dependence is therefore a crucial test for models that describe the cosmic ray transport in the inner heliosphere.

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“…Figure 3 compares modeled O* energy spectra at Earth ( r = 1 AU; θ = 90°) for both the qA < 0 (solid line) and qA > 0 (dashed line) HMF configurations. Shown for comparison are qA > 0 observations for O* at/near Earth from the SAMPEX (downward triangles) [from Hill et al , 2002] and SOHO (squares) [from Marsden et al , 1999] spacecraft and qA < 0 observations of the STEREO (dots) and the ACE (upward triangles) spacecraft [both from Cummings et al , 2009]. The computed spectra show the general characteristics of ACR spectra in the inner heliosphere, for example, an almost exponential decay in intensity above ∼10 MeV nuc −1 and the well‐known j ∝ E increase in intensity below ∼10 MeV nuc −1 caused by adiabatic energy losses.…”

Section: Modeling Resultsmentioning

confidence: 99%

“…Computed O* energy spectra at Earth ( r = 1 AU; θ = 90°) for the qA > 0 (solid line) and qA < 0 (dashed line) HMF polarity cycles. For comparison O* observations at/near the Earth in the qA > 0 cycle, made by the SAMPEX (downward triangles) [from Hill et al , 2002] and SOHO (squares) [from Marsden et al , 1999] spacecraft and qA < 0 observations of the STEREO (dots) and the ACE (upward triangles) [both from Cummings et al , 2009] spacecraft are shown.…”

Section: Modeling Resultsmentioning

confidence: 99%

“…Last, new observational values of the O* gradient in both polarity cycles are currently available, allowing a comparison between computed and observed gradients. A curious feature of the observed latitudinal gradients is that Cummings et al [2009] observed a very small (consistent with a zero gradient but not excluding a positive gradient) latitudinal gradient in the present (the qA < 0) polarity cycle. An explanation for this observation will be presented.…”

Section: Introductionmentioning

confidence: 80%

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Modeling anomalous cosmic ray oxygen gradients over successive solar cycles

Strauss

Potgieter

2010

J. Geophys. Res.

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[1] Cosmic ray drift directions depend both on the charge of the particle population under consideration, as well as the heliospheric magnetic field polarity which oscillates within a ∼22 year cycle. The differences in the cosmic ray drift patterns between successive solar cycles manifest themselves in the sign of the latitudinal cosmic ray gradient. For positively charged particles, a positive latitudinal gradient is expected in the qA > 0 polarity cycle, while a negative value is expected in the qA < 0 cycle. For the first time observed radial and latitudinal values for anomalous cosmic ray oxygen are available in both of these cycles. In the present qA < 0 cycle, the observations seem, however, inconsistent with the drift-dominated considerations discussed above, as the latitudinal gradient is smaller than expected and perhaps even positive. This issue is addressed by using a comprehensive numerical model for anomalous cosmic ray acceleration and transport, based on new diffusion coefficients, to simulate these gradients over the previous two magnetic polarity cycles. Computed gradients and energy spectra (at Earth and at Ulysses) are compared to observations, with good agreement achieved between observations and model predictions. For the qA > 0 cycle, the model predicts a positive latitudinal gradient but for the qA < 0 cycle a latitudinal gradient that is smaller and that can be either positive or negative. It is concluded that drifts and poleward diffusion set up competing latitudinal gradients in the qA < 0 cycle, with the resulting sign of the gradient determined by the most effective of the two processes.Citation: Strauss, R. D., and M. S. Potgieter (2010), Modeling anomalous cosmic ray oxygen gradients over successive solar cycles,

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Radial and latitudinal gradients of anomalous cosmic ray oxygen in the inner heliosphere

Cited by 11 publications

References 26 publications

Solar Modulation of Cosmic Rays

Solar Modulation of Cosmic Rays

Spatial gradients of GCR protons in the inner heliosphere derived fromUlyssesCOSPIN/KET and PAMELA measurements

Modeling anomalous cosmic ray oxygen gradients over successive solar cycles

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