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Intensity Gradients of Anomalous Cosmic Ray Oxygen Throughout the Heliosphere

Cummings, A. C. and Stone, E. C. and Klecker, B. and Marsden, R. G. and Mewaldt, R. A. and Reames, D. V. and Trattner, K.J. and von Rosenvinge, T. T. and Webber, W. R. (1997) Intensity Gradients of Anomalous Cosmic Ray Oxygen Throughout the Heliosphere. In: Proceedings of the 25th International Cosmic Ray Conference. Vol.2. Potchefstroom University, Space Research Unit , Transvaal, South Africa, pp. 257-260.

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We use anomalous cosmic ray oxygen energy spectra collected from five different locations in the heliosphere during three time periods to estimate the radial and latitudinal gradients of the particle intensities at three energies. The three periods include the two high-latitude passes of Ulysses over the solar poles and the last few months of the cosmic ray oxygen data from Pioneer 10. The radial gradient is modeled as a power law in radius and the latitudinal gradient is assumed to be constant. The gradients are analyzed in two ways: the first uses the actual average spacecraft latitudes and the second assumes the symmetry plane of the heliosphere is at 10° S in heliolatitude. Reasonable fits are obtained under either assumption concerning the location of the symmetry plane, although the latitudinal gradients are smaller by a factor of~ 2 if the symmetry plane is offset by l0° S. The radial gradient exhibits a radial dependence of ~r^(-1) or r^(-2) depending on whether the symmetry plane is the helioequator or not, respectively. The r^(-2) dependence is not consistent with the gradient measured in a similar part of the solar cycle ~20 years ago, suggesting that the helioequator is the likely plane of symmetry for these particles. The only significant difference in oxygen flux between polar passes occurs at < 10 Me V /nuc and is similar to that observed one year earlier in the outer heliosphere due to decreasing solar modulation.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Cummings, A. C.0000-0002-3840-7696
Stone, E. C.0000-0002-2010-5462
Mewaldt, R. A.0000-0003-2178-9111
Additional Information:© Space Research Unit. Provided the NASA Astrophysics Data System. This work was supported in part by NASA under contracts NAS7-918 and NASS-30704 and at the Max-Planck-Institut by the Bundesministerium fur Forschung und Technologie, Germany, under contract 50 OC 90021.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Max-Planck-Institut by the Bundesministerium fur Forschung und Technologie, Germany50 OC 90021
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Space Radiation Laboratory1997-08
Record Number:CaltechAUTHORS:20140703-225449871
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46858
Deposited By: Deborah Miles
Deposited On:11 Jul 2014 04:22
Last Modified:20 Feb 2020 14:33

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