Figure 1: (a) Maximum percentage difference between and as a function of the solar distance inside the colatitude regions ( ), ( ), and ( ). (b) Maximum value allowed of as a function of colatitude: values in the “allowed” region guarantee that the stream line originated from the polar magnetic field do not cross the equatorial plane. Since (5) is symmetric with respect to the solar equatorial plane, values greater than of colatitude lead to same results of those presented.