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10 20 30 40 50 60 70 Tilt Angle (degrees)

Fig. 2.37.3. Comparison of intensity-tilt profiles from a two-dimensional and a three-dimensional models for 1.9 GeV protons at the Earth's orbit. From Burger and Potgieter (1999).

In Fig 2.37.3 a different diffusion tensor is used, and the boundary is set at 40 AU. The convergence of the intensity-tilt profiles in the three-dimensional model to a common value is somewhat faster than in the two-dimensional model. Note, however, that the difference between the A > 0 intensities at a tilt angle of 70° is less than 5%. Clearly the two models show the same qualitative behavior, and to a large extent the same quantitative behavior, as the tilt angle increases (Ferreira et al., 1999a; see also below, Section 2.39).

2.37.4. Tilt angle dependence of CR intensity ratios at Earth orbit

The tilt angle and solar polarity-sign dependence of the ratios e-/He++ and e-/p are shown in Fig. 2.37.4, normalized with respect to the minimum value for each ratio. Although there are some quantitative differences between the two ratios, their qualitative behavior is the same. During an A > 0 cycle, the ratio has a 'w' shape, and shows smaller changes when the tilt angle changes than during an A < 0 cycle, when the ratio has an 'm' shape.

A > 0

A< 0

—*--3 GV

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