Relationship between Growing Speed and Turret Development

On the basis of conducting simultaneous observations of cumulonimbi using the X-band radar, and photogrammetry, several cases of cumulonimbus initiations were observed during the mid-summer days from 2010 to 2011 in the southern Kanto region of Japan. The relationship between the maximum growing speed and the maximum height of 40 turrets was almost linear. The average maximum growing speed was 7 m/s. Turrets were categorized into two groups based on their growing speed, relative to this value. The first, named the “inactive” group, consists of turrets that have a relatively low growing speed with a maximum growing speed that is less than 8.5 m/s, and reach up to 8 km AGL. Another group is the “active” group, in which the turrets develop vertically (10 km or more AGL) with a larger maximum growing speed (> 8.5 m/s). In the active group, some turrets grew with a maximum growing speed that was greater than 15 m/s and had a maximum height that was recorded as greater than 10 or 15 km AGL. The turrets that developed over the Boso Peninsula, Japan, during the observation period indicated that the generation area moved northward as time progressed and turrets eventually developed in the northern regions of the Boso Peninsula.