Figure shows the time variation of the number concentration of droplets larger than 3.5 µ m in diameter in a period of up to 150 min. The lighter shade area corresponds to the first NaCl injection period beginning at 53 min as shown in Fig. . The darker area indicates the duration of the increase in the droplet number concentration induced by the NaCl injection. It is found that the increase in the number concentration began after about 10 min from the start of the NaCl injection, and the injection for 20 min brought about the droplet number increase lasting for 45 min. This means that because of turbulence in the updraft, droplets are carried along various different pathways and consequently experience different travel times before they arrive at the top. Since the travel time coincides with the growth time, droplets arriving later should be larger than those arriving sooner. This was actually observed by recording the time variations of the number concentration of droplets classified according to their sizes.