Snapshots of the vertically integrated current for the twisted field at t = 0a), t = 4.9b) and t = 9.8c). In a) we see the Z-sigmoidal shape of the initial tube. b) Shows that the tube’s outer current layer has expanded. In c) the outer shell has further expanded leaving an inner rope structure which is far less kinked than in a). The rotation of the tube core from a) to c) is counter-clockwise.