Propagation speed (a) and acceleration (b) of LE of the selected CMEs derived from the GCS-model-fitted 3D LE heights. (c) Height-time profiles of the CMEs assuming no acceleration (solid line) and some value of a constant average deceleration (dashed line). The color-filled circles indicate the first possible CME-CME interaction height. The initial dots show the GCS-fitted heights for the CMEs. We include only every other data point for the GCS-fitted heights for the sake of clarity.