The simulated features of heliospheric cosmic-ray modulation with a time-dependent drift model. II - On the energy dependence of the onset of new modulation in 1987

1992 ◽  
Vol 390 ◽  
pp. 661 ◽  
Author(s):  
J. A. Le Roux ◽  
M. S. Potgieter
2005 ◽  
Vol 23 (3) ◽  
pp. 1061-1070 ◽  
Author(s):  
D. C. Ndiitwani ◽  
S. E. S. Ferreira ◽  
M. S. Potgieter ◽  
B. Heber

Abstract. Time dependent cosmic ray modulation in the inner heliosphere is studied by comparing results from a 2-D, time-dependent cosmic ray transport model with Ulysses observations. A compound approach, which combines the effects of the global changes in the heliospheric magnetic field magnitude with drifts to establish a realistic time-dependence, in the diffusion and drift coefficients, are used. We show that this model results in realistic cosmic ray modulation from the Ulysses launch (1990) until recently (2004) when compared to 2.5-GV electron and proton and 1.2-GV electron and Helium observations from this spacecraft. This approach is also applied to compute radial gradients present in 2.5-GV cosmic ray electron and protons in the inner heliosphere. The observed latitude dependence for both positive and negative charged particles during both the fast latitude scan periods, corresponding to different solar activity conditions, could also be realistically computed. For this an additional reduction in particle drifts (compared to diffusion) toward solar maximum is needed. This results in a realistic charge-sign dependent modulation at solar maximum and the model is also applied to predict charge-sign dependent modulation up to the next expected solar minimum.


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