Observed Variation of Three-Dimensional Return Stroke Speeds Along the Channel in Rocket-Triggered Lightning

Abstract

An improved very high frequency location system, multiple antenna radiation continuous observation system (MARCOS), is combined with high-speed video observation to explore radiation source evolution during return stroke (RS) stages in triggered lightning. A three-dimensional (3-D) channel reconstruction is performed for speed measurement of the RS processes. The 3-D average speeds for the two selected strokes (RS1 and RS3) over the bottom channel within 1 km are 9.24 × 107 m/s and 1.07 × 108 m/s, respectively. The high temporal-spatial resolution of MARCOS permits thorough examination of the speed variation. Our observation shows that the 3-D RS speeds of both RS1 and RS3 are increased initially with height for the first several hundred meters, maximized, and then decreased with height. To the best of our knowledge, this is the first evidence regarding nonmonotonic 3-D RS speed variation in triggered lightning.