An analysis of the initiation of upward flashes from tall towers with particular reference to Gaisberg and Säntis Towers

• Upward flashes from the Gaisberg and the Säntis Towers are mostly self-initiated.
• Polarity of triggered and preceding events varies for different towers.
• Upward flash initiation features a strong seasonal variation depending on location.
• All towers have similar time intervals between preceding and triggered lightning.

In this paper, we present an analysis of the lightning events preceding initiation of upward lightning flashes from the Gaisberg and the Säntis Towers. It is found that the majority of upward lightning discharges from both towers are initiated without any preceding lightning activity. We show also that the results of the presented studies on the initiation of upward flashes from tall structures might be affected by the selected parameters of the study, namely the time and distance intervals used to identify the triggering events. Preceding events had the same polarity as triggered flashes in the case of the Säntis Tower and had opposite polarities in the case of the Gaisberg Tower. The effect of seasonal and temperature variations have been also analyzed.