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Characteristics of sunward flowing proton and alpha particle fluxes of moderate intensity

Marshall, F. E. and Stone, E. C. (1978) Characteristics of sunward flowing proton and alpha particle fluxes of moderate intensity. Journal of Geophysical Research A, 83 (A7). pp. 3289-3298. ISSN 0148-0227. doi:10.1029/JA083iA07p03289.

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The diffusive streaming of 1.3- to 2.3-MeV per nucleon protons has been found to be predominantly toward the sun during periods between prompt solar particle events. This sunward streaming occurs for essentially all proton intensities from <0.012 to 1.2 (cm^2 s sr MeV)^−1 and for all solar wind velocities. The average radial component (16% ± 3%) of the diffusive anisotropy of 1.4- to 2.4-MeV per nucleon alpha particles is very similar to that observed for protons (14% ± 1%), a finding suggesting a common origin. These periods are characterized by a limited variance in the proton intensities (10^(−1.2±1.1) cm^-2 s^-1 sr^−1 MeV^−1), in the proton spectra (E−3.0±0.8), and in the α/p ratio (3% ± 2%). The sunward diffusion of protons and alpha particles indicates that a positive radial gradient is characteristic of these modestly enhanced fluxes. A steady state propagation model which includes adiabatic energy loss and a source of particles beyond 1 AU produces the average radial anisotropy and its dependence on the solar wind velocity for κ_rr ∼ 4 × 10^20 cm^2 s^−1. The direction of the diffusive anisotropy is strongly dependent on the magnetic field direction, a situation indicating κ⊥ < κ∥. However, the two directions are not identical, a condition indicating nonnegligible flow perpendicular to the average field direction when averaged over a 6-hour interval.

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Stone, E. C.0000-0002-2010-5462
Additional Information:© 1978 by the American Geophysical Union. Received July 18, 1977; revised January 19, 1978; accepted February 8, 1978. We are grateful to H. S. Bridge and J. D. Sullivan for providing Imp 7 plasma date prior to publication. We are also grateful to R. E. Vogt, who has been intimately involved throughout the Imp 7 program. Significant contributions to this project have also been made by W. E. Althouse, G. J. Hurford, and R. A. Mewaldt. This work was supported in part by the National Aeronautics and Space Administration under contract NAS5-11066 and grant NGR 05-002-160. F. E. Marshall has received valuable support from an NDEA fellowship.
Group:Space Radiation Laboratory
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NASANGR 05-002-160
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory1977-03
Issue or Number:A7
Record Number:CaltechAUTHORS:20140205-114447575
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Official Citation:Marshall, F. E., and E. C. Stone (1978), Characteristics of sunward flowing proton and alpha particle fluxes of moderate intensity, J. Geophys. Res., 83(A7), 3289–3298, doi:10.1029/JA083iA07p03289.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43674
Deposited On:05 Feb 2014 22:45
Last Modified:10 Nov 2021 16:41

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