Lightning attachment process parameters measured by using LAPOS

Using a high speed optical imaging system called LAPOS, we have observed the lightning attachment processes of 19 negative and 2 positive CG. We have obtained not only their stepped leader speeds and the return stroke speeds near the channel bottoms, but also their return stroke initiation heights. Most of the negative first return strokes exhibited an initiation height of 40 m or so. Return strokes with bigger peak current tend to initiate higher. For one positive first stroke, although its peak current is much larger than all the negative counterparts, its initiation height is smaller than most of the negative ones.