Meteorological Aspects of Self-Initiated Upward Lightning at the Santis Tower (Switzerland)

Interest in exploring the meteorological conditions favoring upward lightning from tall man-made structures has grown in recent years, largely due to the worldwide expansion of wind energy. To this end, instrumented towers existing around the world are the most suitable places to study upward lightning. In this context, an LMA network was deployed around the Santis Mountain (northeast Switzerland) during the summer of 2017, in order to complement the long-term measurements currently held at the Santis telecommunications tower, a lightning hot spot in central Europe. This campaign allowed, for the first time, to gather a comprehensive set of observations of self-initiated upward lightning emerging from the Tower. With the help of C-band dual-polarimetric radar data, the present work focuses on the meteorological conditions conductive to self-initiated upward lightning from the Santis. The analysis revealed that the upward propagating positively charged leaders spread mostly horizontal above the melting level, after an initial short vertical path from the tower tip. After this initial stage, the majority of upward leaders were followed by a sequence of negative return strokes. The inception upward lightning under a stratiform cloud shield would be favored by the low height of the charge structure. From the obtained results, it turns out that a key feature favoring self-initiated upward lightning would be the proximity of the tower tip to the melting level.