(a) Initial potential magnetic field. The field is symmetric about the axis of rotation and the equator, so only one quadrant is shown. The photospheric boundary surface is indicated by the light gray grid. Magnetic field lines are colored (red, green, or blue) according to their flux system. Two types of blue field lines are indicated, higher lying light blue unsheared field and low‐lying dark blue field that is sheared later in the simulation. (b) Force‐free field after a shear of π/8. The field lines shown correspond to those in (a) and are traced from the same footpoint position on the photosphere as in (a). (c) As above, but for a shear of 3π/8. (d) As above, but for a shear of π/2.