Current waveforms associated with positive flashes recorded on the Säntis tower in summer 2010

We present in this paper measured current waveforms associated with positive flashes recorded on the Säntis tower, Switzerland, in Summer 2010. About 20% of the recorded flashes were of positive polarity (transported positive charge to ground), all of them being recorded in July and August. This percentage is considerably larger than the values observed in other studies in summer months (3% to 6.5%). The observed current waveforms can be classified into two types. The first type is characterized by three stages: (1) an initial, slowly rising portion lasting a few milliseconds, (2) the main pulse, and (3) a long continuing current that may contain several pulses of both polarities characteristic of M components. The second type of observed positive flashes is characterized by (i) the absence of any initial slowly rising portion, (ii) lower peak currents, and (iii) presence of successive pulses which may be due to an upward stepped leader. The time-derivatives of the current pulses associated with upward stepped leaders are found to be much larger than those of the main pulse. All the observed flashes contained a single main pulse, except for one flash of the second type, which featured two pulses. Our recorded data constitute the first directly-measured evidence of M-components of both polarities during a continuing current lowering positive charge to ground.