Sample BP before and during CJ ejection process. The top three rows represent overlap of SDO/AIA 193, 304, and 171 Å intensity images and SDO/HMI photospheric magnetograms. The bottom row represents HMI magnetogram separately. Blue and yellow contours indicate positive and negative magnetic field polarities, respectively. These regions are also indicated with arrows in the bottom row of panel (a). Panel (a): the beginning of precursor; panel (b): the peak of the precursor brightening; panel (c): the time after the precursor when still there is no signature of main jet outflow; panel (d): the moment when the structure is destabilized and the jet-type instability starts; panel (e): the fully developed transient jet outflow. In panel (e), we take a wider observational window as shown on the corresponding axes.