Fig.2.36.1. Radial dependence of the radial and polar mean free paths, and the drift scale for 1 GV protons in the ecliptic and at 10° colatitude (upper panels). The two lower panels show the rigidity dependence of the same variables at a radial distance of 3 AU. In all cases Y = n = -0.4. From Burger et al. (1999).
From the panel (a) in Fig. 2.36.1 can be seen that in the ecliptic region Arr approaches Aqq beyond 30 AU. Radial diffusion is dominated by K at large radial distances where the field becomes azimuthal, and in the ecliptic region K = Kee. In the polar region (see panel (b) in Fig. 2.36.1), Aqq exceeds A at large radial distances where K again begins to dominate radial diffusion; but here
K < Kee . The panels (c) and (d) in Fig. 2.36.1 show that the polar mean free path has a flatter rigidity dependence than the radial mean free path. Drifts are slightly reduced (below about 1 GV) with respect to the weak scattering case which is proportional to R at all rigidities.
The parameters y = n = -0.4 in Eq. 2.36.5 are chosen to fit solar minimum data at Earth for both solar polarity epochs, by changing only the sign of the magnetic field. Although optimized for protons, good fits to galactic helium and high energy electrons are also obtained.
The central result of paper Burger et al. (1999) is Fig. 2.36.2, which shows a comparison of the latitudinal gradient for CR protons calculated at 2 AU between the ecliptic and 10° colatitude, and Ulysses data.
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