Rapid evolution of energetic lightning strokes in Mediterranean winter storms

The occurrence of winter lightning concentrates in a few specific regions in the world, including the Mediterranean, where electromagnetic signatures of this interesting dangerous phenomenon have not yet been studied in detail. We investigate the initial stage of energetic negative cloud-to-ground winter lightning flashes in the West Mediterranean region using broadband magnetic field measurements (5 kHz–90 MHz) recorded in winter 2014/2015, which was unusually rich in global lightning activity. We found that the winter pre-stroke processes leading to the high peak current lightning (<−100 kA) lasted on average only 1.7 ms (in one case only 220 µs). Rapid evolution of energetic lightning indicates that leader initiation charge centers can be as low as 500 m above the ground. The measured distribution of pre-stroke pulse amplitudes and interpulse intervals can be used to model the charge structure in the lower thundercloud dipole and to derive the properties of in-cloud lightning channels.