Observation and properties of a sub-cloud bidirectional leader

In this paper we present the evolution of a bidirectional leader which appeared in ‘virgin’ air. In the observations we did not find any delay between the onsets of the two leader ends. The positive leader end presented a single channel, brighter and slower than the negative end. On the other side, the negative end was branched, less bright and twice as fast as the positive end. The attachment of one of the negative channels with a pre-existing intra-cloud channel showed that the polarity reversal point in the bidirectional leader remained fixed. Recoil leaders appeared along old negative channels of the bidirectional leader. Recoil activity started after the first branching of the positive leader. The discussion is aimed at improving current bidirectional leader models.Postprint (published version

Global distribution of winter lightning: a threat to wind turbines and aircraft

Lightning is one of the major threats to multi-megawatt wind turbines and a concern for modern aircraft due to the use of lightweight composite materials. Both wind turbines and aircraft can initiate lightning, and very favorable conditions for lightning initiation occur in winter thunderstorms. Moreover, winter thunderstorms are characterized by a relatively high production of very energetic lightning. This paper reviews the different types of lightning interactions and summarizes the well-known winter thunderstorm areas. Until now comprehensive maps of global distribution of winter lightning prevalence to be used for risk assessment have been unavailable. In this paper we present the global winter lightning activity for a period of 5 years. Using lightning location data and meteorological re-analysis data, six maps are created: annual winter lightning stroke density, seasonal variation of the winter lightning and the annual number of winter thunderstorm days. In the Northern Hemisphere, the maps confirmed Japan to be one of the most active regions but other areas such as the Mediterranean and the USA are active as well. In the Southern Hemisphere, Uruguay and surrounding area, the southwestern Indian Ocean and the Tasman Sea experience the highest activity. The maps provided here can be used in the development of a risk assessment.Peer ReviewedPostprint (published version

Basic lightning flash properties derived from lightning mapping array data

The size and duration of lightning flashes are examined. Data from the Ebro Valley Laboratory Lightning Mapping Array is used as reference. Additional data from the VLF/LF LINET network is included. In the analysis, each flash is simplified by a confidence ellipse fitting most of the detected sources. The major axis of the ellipse is adopted as the flash length. Flash durations are computed too. The analysis of 778 flashes results in a median flash length of ¿14 km with a median duration of ¿0.3 s. The results presented, besides characterizing the storm activity, they can be useful to define stroke grouping criteria, lightning flash density calculations and lightning warning purposes.Postprint (published version

Charge structure analysis of a severe hailstorm with predominantly positive cloud-to-ground lightning

Peer ReviewedPostprint (author's final draft

Charge structure analysis of a severe hailstorm with predominantly positive cloud-to-ground lightning

Peer Reviewe

Observation and properties of a sub-cloud bidirectional leader

In this paper we present the evolution of a bidirectional leader which appeared in ‘virgin’ air. In the observations we did not find any delay between the onsets of the two leader ends. The positive leader end presented a single channel, brighter and slower than the negative end. On the other side, the negative end was branched, less bright and twice as fast as the positive end. The attachment of one of the negative channels with a pre-existing intra-cloud channel showed that the polarity reversal point in the bidirectional leader remained fixed. Recoil leaders appeared along old negative channels of the bidirectional leader. Recoil activity started after the first branching of the positive leader. The discussion is aimed at improving current bidirectional leader models

Total lightning detections of lightning flashes recorded by means of high-speed videos

A detailed analysis of two lightning flashes is presented. High speed video, total lightning detections and electric field measurements are the basis of the study. In general, the observed negative cloud-to-ground flashes do not produced many VHF detections . In the negative flash, most of the detections are given in the fast increase of electric field at the beginning of the dart leader. An intriguing feature during negative leaders is the fast illumination of some branches especially at the time when the leader is approaching the ground. In the case of positive cloud-to-ground flashes, a frenetic recoil leader activity occurs before the return stroke. In the presented case, recoil leader rates increase before the return stroke. The VHF network reported a large amount of detections. Those detections are not correlated with recoil leaders but with continuous current transfer to the ground

Total lightning detections of lightning flashes recorded by means of high-speed videos

A detailed analysis of two lightning flashes is presented. High speed video, total lightning detections and electric field measurements are the basis of the study. In general, the observed negative cloud-to-ground flashes do not produced many VHF detections . In the negative flash, most of the detections are given in the fast increase of electric field at the beginning of the dart leader. An intriguing feature during negative leaders is the fast illumination of some branches especially at the time when the leader is approaching the ground. In the case of positive cloud-to-ground flashes, a frenetic recoil leader activity occurs before the return stroke. In the presented case, recoil leader rates increase before the return stroke. The VHF network reported a large amount of detections. Those detections are not correlated with recoil leaders but with continuous current transfer to the ground.Postprint (published version

Total lightning detections of lightning flashes recorded by means of high-speed videos

A detailed analysis of two lightning flashes is presented. High speed video, total lightning detections and electric field measurements are the basis of the study. In general, the observed negative cloud-to-ground flashes do not produced many VHF detections . In the negative flash, most of the detections are given in the fast increase of electric field at the beginning of the dart leader. An intriguing feature during negative leaders is the fast illumination of some branches especially at the time when the leader is approaching the ground. In the case of positive cloud-to-ground flashes, a frenetic recoil leader activity occurs before the return stroke. In the presented case, recoil leader rates increase before the return stroke. The VHF network reported a large amount of detections. Those detections are not correlated with recoil leaders but with continuous current transfer to the ground

Lightning flash properties derived from lightning mapping array data

in this paper size and duration of lightning flashes are examined. Data from the Ebro Valley Laboratory Lightning Mapping Array is used as reference. Additional data from the VLF/LF LINET network and meteorological radar is included. In order to simplify the complex geometry of a lightning flash, each flash is described by a confidence ellipse fitting most of the detected sources. The flash length is represented by the major axis of the ellipse. The analysis of 778 flashes results in a median flash length of 14 km with a median duration of 0.3 s. The results presented here, besides characterizing the storm activity, provide valuable information in order to improve the stroke grouping criteria in the flash algorithm, lightning flash density calculations and lightning warning procedures.Peer ReviewedPostprint (published version