A prominence-cavity system on the Sun. The magnetic field lines are colored by temperature and three LOSs are marked by the three arrows. The location of the middle vertical slice (at which various quantities are later plotted in Figure 3) in the system is marked by the red-dashed line. In order to show the three LOSs, we rotate the coordinate system, with the y-axis as the rotation axis, and show the prominence-cavity system on the top of the figure, with the z-axis shown in the legend pointing toward the north pole. The units of the coordinate axes are in solar radius.