Positive lightning flashes recorded on the Säntis tower from May 2010 to January 2012

Abstract

We analyze currents of 30 positive flashes recorded on the Säntis tower, Switzerland, from May 2010 to January 2012. The currents were classified into two types. Type 1 events exhibit a large, unipolar main pulse with a risetime of tens of microseconds, followed by subsidiary peaks separated by millisecond-scale intervals. The main pulse in three flashes was preceded by a slowly rising ramp lasting several milliseconds and was followed by a relatively steady current with superimposed positive and negative pulses, constituting the first direct evidence of M components of both polarities. In four of the five type 1 flashes, the main current was preceded by pulse bursts, presumably due to attempted negative leaders. Type 2 events are characterized by a millisecond-scale waveform with large, oscillatory pulse trains on its rising portion. These pulse trains are inferred to be due to upward negative stepped leaders. Peak currents of type 2 flashes are associated with the fast pulses. Our positive flashes of both types have a median peak current of 11.1 kA and a median duration of 80 ms, consistent with data recorded in Austria. Our measured median transferred charges are about 6 times larger than those at Switzerland's Monte San Salvatore and in Japan and about 3 times larger than in Austria. Eight type 2 flashes in our data set transported over 500 C of positive charge to ground. Our five type 1 events appear to be similar (except for the pulse duration) to their counterparts examined by Berger et al. (1975). Our type 2 events are "classical" upward flashes. Key Points An analysis is presented of currents from positive flashes to the Säntis tower Two types of positive flashes were observed and characterized The median transferred charge is much larger than in other instrumented towers ©2013. American Geophysical Union. All Rights Reserved.