Positive Vx is earthward flow. The vertical black line is centered on the zero crossing of Bz. The increase in total pressure to above the lobe pressure is a common feature of flux ropes and implies a strong curvature force. We assume that the motion of the flux rope is entirely in the x direction. In the next figure we have isolated the Bz signature from ISEE2.
Green lines demark the leading and trailing edges.
The flux rope is embedded in a plasma sheet with finite Bz. Bz behind the flux rope is larger than in front, due to the BBF behind the flux rope, pushing it earthward, and piling up flux. The bottom 2 drawings show what might happen to a flux rope embedded in a plasma sheet with finite Bz, with the earth to bottom left of both figures. These field lines are anti-parallel to the flux rope field lines at the leading edge. There are several ways in which the temperature of a plasma can decrease.