Example of two MCs in interaction. Magnetic cloud 44 is a large MC with a strong magnetic field; it is interacting with the smaller MC 26 (the vertical dashed lines define the MC boundaries). The magnetic field rotation is mostly in the longitude of the field (Φ_B) for MC 44 and mostly in the latitude of the field (θ_B) for MC 26 wich implies that the MC axis are almost orthogonal to each other. Nevertheless there is only a weak change in the magnetic field between the outward branch of MC 44 and the inward branch of MC 26. The MCs are separated by a sheath-like region with a magnetic field of different orientation. The bottom panel shows that MC 26 is not expanding. A linear least squares fit of the velocity is indicated by a green line in the time interval where an almost linear trend is present in each MC.