Characteristics of upward bipolar lightning flashes observed at the Gaisberg Tower

Abstract

We analyze current records for 21 upward initiated bipolar lightning flashes observed at the Gaisberg Tower (GBT) in Austria from 2000 to 2009. A bipolar lightning flash occurrence of 3% (21/652) is found during the 10‐year observation period. Thirteen (62% or 13/21) of them occurred in nonconvective season (September–March). On the basis of the classification suggested by Rakov and Uman (2003), 13 (62%) of the 21 bipolar flashes belong to Type 1 associated with a polarity reversal during the initial stage (IS) current, five belong to Type 2 associated with different polarities of the IS current and the following return strokes, one belongs to Type 3 associated with return strokes of opposite polarity following the IS, and two of them are not assigned. We also find that the initial polarity reversal from negative to positive occurs more often (76% or 16/21) than that from positive to negative within a bipolar flash, in agreement with observations in other studies. The geometric mean (GM) and arithmetic mean (AM) of the total absolute charge transfer are 99.5 C and 125 C, with the GM and AM total flash duration of 320 ms and 396 ms, respectively. From simultaneous current and high‐speed video measurements of one bipolar flash, within the field of view, the positive charge was transferred along one branch initially, followed by the negative charge transfer after cessation of the luminosity for 142 ms, while the other two branches connected to the main channel always contributed to the negative charge transfer during the whole process.

Characteristics of upward positive lightning flashes initiated from the Gaisberg Tower

“…In section 3.2 of this paper we have defined various parameters of interest during upward negative leader process. Figure 9 shows the histogram of leader pulse train duration ( t tot ) in 22 upward positive (red bars) flashes and 3 upward bipolar (blue bars) flashes with positive initial current polarity (see flashes GBT 402, GBT 646, and GBT 653 from Zhou et al [2011, Table 1]). Flashes GBT 288, GBT 329, GBT 382, and GBT 383 from Table 1 in this paper were excluded because of unpronounced and undetectable current pulses (they do have similar current pulses superimposed on the initial continuous current but with relatively lower amplitudes).…”

Some characteristics of positive and bipolar lightning flashes recorded on the Säntis tower in 2010 and 2011

“…This number is lower than those reported in previous studies in Austria (3%, [24]) and in Monte San Salvatore (6%, [25]). All three flashes occurred in the morning of August 27, 2011.…”

Burst of intracloud current pulses during the initial continuous current in a rocket‐triggered lightning flash

“…Therefore, it merits further efforts to conduct same measurements for ICC of varying magnitude in triggered lightning. Also, the initial continuous current is commonly observed in triggered lightning from tall objects [ Miki et al ., ; Flache et al ., ; Zhou et al ., ]. Hence, it is of particular interest to implement contemporary magnetic field measurements to see whether the ICC process in object‐initiated lightning could also be associated with the similar burst of magnetic pulses as observed in this particular event.…”