Height-dependent attenuation characteristics of lightning return strokes

We have studied the height-dependent attenuation characteristics of return stroke peak light intensities within the lowest tens of meters of the lightning channel. It was found that all return strokes follow a similar height-dependent attenuation tendency (decrease in light intensity peak amplitude and increase in rise time) in their upward propagation. While in their downward propagation, although 10 out of 11 return strokes decreased their light intensity amplitudes, only 3 out of 11 return strokes have exhibited an increased rise time. The attenuation within the lowest tens of meters of the lightning channel tends to be much stronger than that over the remaining propagation.