We investigated features of corona point discharges when a grounded conductive rod is subject to a high background electric field. In the laboratory, high voltage is applied to an upper plate in a plane-to-point experiment, and the discharges are observed from a grounded rod using an ultraviolet camera and a photosensor. The current is measured using a shunt resistor, a current transformer, and a high impedance ammeter. We have found that corona current pulses have fast rise time (tens of nanoseconds) and slow decay (hundreds of nanoseconds). For the initial stage of the discharges, above a certain threshold, the frequency of pulses increases with the voltage applied. In the field, one current sensor coupled to a grounded rod, 1.5 m above a roof, was installed in a site located at an altitude of 2525 m above sea level. The same pulses observed in the laboratory are recorded during periods of electric field enhancement caused by the movement of charged clouds or lightning activity near the sensor. For that specific installation, the frequency of pulses is correlated with the ambient electric field measured 250 meters away. To the best knowledge of the authors, this is the first time in which such correlation is made for outdoor measurements, seeing that other works correlate the electric field with the average current flow. Pulses of positive corona were no longer observed when the electric field magnitude was lower than 1.8 kV/m and pulses of negative corona were more atypical and presented a higher threshold, of about 3.8 kV/m. This study is relevant for understanding the production of corona and space charges in high structures, such as wind turbine blades, towers, and buildings in general.

The development of downward and upward leaders that formed two negative cloud‐to‐ground return strokes in natural lightning, spaced only about 200 µs apart and terminating on ground only a few hundred meters away, was monitored at Morro do Cachimbo Station, Brazil. The simultaneous records of current, close electric field, relative luminosity, and corresponding high‐speed video frames (sampling rate of 20,000 frames per second) reveal that the initiation of the first return stroke interfered in the development of the second negative leader, leading it to an apparent continuous development before the attachment, without stepping, and at a regular two‐dimensional speed. Based on the experimental data, the formation processes of the two return strokes are discussed, and plausible interpretations for their development are provided.

This work presents the first simultaneous X‐ray measurements from natural lightning in coincidence with a very high frequency (VHF) broadband interferometer. During an observational campaign in north‐central Colombia, five intense X‐ray bursts were detected from negative stepped leaders and two X‐ray emissions from a dart leader. Thanks to the high angular and time resolution of the interferometer, it was possible to locate the origin of high‐energy radiation during the lightning leader propagation. We study the correlation with VHF pulses and the two‐dimensional speed of the leader channels. A strong temporal correspondence has been observed between the high‐energy emissions and the most intense VHF pulses, which suggests the runaway electrons as a shared mechanism. The observations show that an X‐ray burst can have multiple high‐energy sources belonging to different leader branches, that can be several hundreds of meters apart. Therefore, from a spatial point of view, not a unique origin has to be searched, but an extensive origin of the X‐ray burst should be considered. We hypothesize similar conclusions in particular for downward TGFs and maybe for TGFs in general.

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