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The simulated features of heliospheric cosmic-ray modulation with a time-dependent drift model. I - General effects of the changing neutral sheet over the period 1985-1990
Potgieter, M. S.; Le Roux, J. A.
AA(NASA, Goddard Space Flight Center, Greenbelt; Maryland, University, College Park), AB(Maryland, University, College Park)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 386, Feb. 10, 1992, p. 336-346. Research supported by University of Maryland and Department of Environmental Affairs of the Republic of South Africa. (ApJ Homepage)
Publication Date:
Space Radiation
NASA/STI Keywords:
Astronomical Models, Galactic Cosmic Rays, Heliosphere, Solar Activity, Interplanetary Medium, Pioneer 10 Space Probe, Solar Magnetic Field, Time Dependence, Voyager 1 Spacecraft, Voyager 2 Spacecraft
Bibliographic Code:


A time-dependent drift model is used to simulate the heliospheric modulation of galactic cosmic rays, with emphasis on the effects of the wavy heliospheric neutral sheet (HNS) as a function of time during the period 1985-1990. The model predicted a clearly defined time difference between the time when minimum modulation occurred at earth and at radial distances farther away from the sun, indicating that the HNS plays an important part in establishing this observed time delay. The movements of the Voyager 1 and 2 and Pioneer 10 spacecraft were simulated in order to calculate instantaneous radial and latitudinal gradients. The time dependencies of these gradients were found to follow the observations well. The model study indicates that the HNS cannot be ignored, especially during periods of low to moderate solar activity, when the modulation of cosmic rays is described.

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