Characteristics of the brief but bright discharges that often occur along the trails of positive leaders

. Characteristics of 273 brief but bright (BB) discharges in 14 upward positive leaders and 75 BB discharges in a downward positive leader documented using a high speed video camera have been studied. On the basis of the two-dimensional (2D) shapes obtained from the high-speed video images, the BB discharges can be grouped into five types. Most of the BB discharges appeared only in one frame of our high speed video, indicating that most of them progress very fast. For those slow progressing BB discharges, some of them are identified progressing at two sides and some only at one side, and their speeds are at the order of 10 6 m/s, similar to that of a typical negative dart-stepped leader. No apparent differences have been found between the BB discharges in upward lightning and in downward lightning. For 3 of the 14 upward lightning flashes, we have recorded their channel base current and electric field changes. We have detected the simultaneous current and electric field change for only 1 BB discharge among 32 discharges contained in the 3 upward lightning flashes. We argue that the BB discharges should not be simply called recoil leaders (RLs). ,