Examples of PFSS extrapolations showing the radial magnetic field component at the outermost surface (2.5 R_⊙) for six different dates, on which the HSB-Earth are predicted to be at central meridian. In the intensity map blue is negative polarity, yellow is positive, with the black line being the sector boundary (neutral line). Over-plotted are the RHESSI flares (red crosses) that occurred within 1 day. The parts of the sector boundary marked with purple points are the HSB, found out to ±40° latitude.