Direct observations of X-rays produced by upward positive lightning.

X-rays have been observed in natural downward cloud-to-ground lightning for over 20 years and in rocket-triggered lightning for slightly less. In both cases, this energetic radiation has been detected during the stepped and dart leader phases of downward negative flashes. More recently, X-rays have also been reported during the dart leader phase of upward negative flashes. In this study, we present the observations of four upward positive lightning flashes from the Säntis Tower (2.5 km ASL) in Switzerland. These consist of the simultaneous records of electric current passing through the tower, and electric field strength and X-ray flux 20 m from the tower base. One of the flashes was captured by a high-speed camera operating at 24,000 frames per second, stills from which are also presented. We detected X-rays during the initial phase of upward negative leader propagation, which can be associated with the leader-stepping process from electric field and current waveforms. To the best of our knowledge, this is the first time that such measurements are reported in the literature. The obtained time-synchronised data confirm that the X-ray emissions detected are associated with the initial steps of the upward negative leader. The frequency and energy of X-ray pulses appear to decrease as functions of time, with pulses disappearing altogether within the first millisecond of the leader initiation. X-ray emission also appears to be correlated with the maximum current-derivative and the electric field change of leader steps, consistent with cold electron runaway. These observations contribute to improving our understanding of upward lightning, which is a primary source of damage to tall structures such as wind turbines and telecommunications towers, as well as aircraft during takeoff and landing.

Laser-guided lightning.

Lightning discharges between charged clouds and the Earth's surface are responsible for considerable damages and casualties. It is therefore important to develop better protection methods in addition to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments-formed in the sky by short and intense laser pulses-can guide lightning discharges over considerable distances. We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Säntis mountain in north-eastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very-high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers. This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures.

[Lightning injuries--a mixture of electrical, thermal and multiple trauma]. / Blixtolyckor--mix av elektriskt, termiskt och multipelt trauma.

There are several misconceptions even among hospital personnel regarding damages and injuries caused by lightning. Few health care providers have experience from lightning injuries as they are rare and different (DC) from the more common high-voltage (AC) injuries. Furthermore, fatalities are uncommon. Burns do occur but are usually minor. Most lightning injuries occur in the summer season during outdoor leisure activities and in the vicinity of a tree or other large structures. In Sweden, on average, approximately seventeen persons per year are hospitalised and 0.2-0.8 persons per million inhabitants and year die due to lightning injuries. The primary treatment follows the general guidelines for other trauma, electrical, and burn injuries, i.e. as is described in the standardised ATLS, ABLS, or A-HLR programmes. However, there are some minor points that are different and may be stressed for a favourable outcome. In this paper these are addressed together with the epidemiology, effects and treatment of lightning injuries that are specific for Sweden. Unfortunately, little is known, apart from what is described in smaller case series, of the long time sequelae experienced by this patient population and further research is therefore particularly warranted in this respect.