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During the night of October 29-30, 2013, a low-light video camera at Pic du Midi (2877 m) in the French Pyrénées, recorded TLEs above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73 °C at ~1600 UTC while its cloud to ground (CG) flash rate reached ~30 fl min-1. Some sprite events with long duration are classified as dancing sprites. We analyze in detail the temporal evolution and estimated location of sprite elements for two cases of these events. They consist in series of sprite sequences with a duration that exceeds 1 second. By associating the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies and the current moment waveform of the lightning strokes, some findings are highlighted: (i) In each series, successive sprite sequences reflect the occurrence time and location of individual positive lightning strokes across the stratiform region. (ii) The longer time-delayed (> 20 ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent stroke (< 200 C km) and they are shifted few tens of kilometres from their SP+CG stroke. However, both short and long time-delayed sprite elements also occur after strokes that produce a large iCMC and that are followed by a continuing current. (iii) The long time-delayed sprite elements produced during the continuing current correspond to surges in the current moment waveform. They occur sometimes at an altitude apparently lower than the previous short time-delayed sprite elements, possibly because of the lowered altitude of the ionosphere potential. (iv) The largest and brightest sprite elements produce significant current signatures, visible when their delay is not too short (~3-5 ms).

The analysis of high-energy background radiation (0.1 – 2 MeV) enhancements during eight winter thunderstorms and ¿ve summer storms in the Ebro delta region in the northeast of Spain is presented. For the ¿rst time, high-energy radiation counts, precipitation, radar re¿ectivity, and very high frequency lightning detections to infer charge regions altitude have been analyzed in order to ¿nd out what produces the measured background radiation increments associated with storms. The good agreement between radar re¿ectivity and precipitation with increases in background radiation counts coupled with the spectrum analysis comparing rain/no rain periods suggests that radon-ion daughters play a major role in the radiation increments reported. No evidence has been found supporting that measured background radiation enhancements can be produced by storm electric ¿elds. Finally, a single case of a high-energy radiation increase was prior to a cloud-to-ground lightning stroke, which reinforces the theory that a lower positive charge layer’s existence is important for the production of Terrestrial Ground Enhancements.

Electromagnetic field from simulated double-headed mid-gap streamers is computed. The effect of the applied electric field is studied by considering electric fields higher than the conventional breakdown threshold (‘overvoltage’). The obtained results show a 20 dB decay at 3.8 GHz for conventional breakdown electric field, 35 GHz for ambient electric fields five times the conventional breakdown and 170 GHz for fields ten times the conventional breakdown electric field. The limitation in nature of the intense electric fields suggest further experiments using a radio receiver at frequencies of more than 10 GHz in order to investigate the origin of the detected x-rays in laboratory sparks.

Earth’s atmospheric potential rapidly increases up to few tens of kilovolts below 200 m altitude. This potential drop will induce charge to tall objects at ground by virtue of electrostatic induction. In this work we investigate the induced electric charges in fair weather to a 1.5 MW and 5 MW wind turbines. The effect of rotation is included and the current calculated result in currents of few micro-amps. The production of point discharge and corona is investigated and some experiments are conducted by means of instrumented kites.

Electromagnetic field from simulated double-headed mid-gap streamers is computed. The effect of the applied electric field is studied by considering electric fields higher than the conventional breakdown threshold (‘overvoltage’). The obtained results show a 20 dB decay at 3.8 GHz for conventional breakdown electric field, 35 GHz for ambient electric fields five times the conventional breakdown and 170 GHz for fields ten times the conventional breakdown electric field. The limitation in nature of the intense electric fields suggest further experiments using a radio receiver at frequencies of more than 10 GHz in order to investigate the origin of the detected x-rays in laboratory sparks.

Lightning involves high energy processes that still are not well understood. In the laboratory voltages pulses are used to produce long sparks allowing the production of energetic radiation. In this paper X-rays emitted by long sparks in air are simultaneously measured with the RF power radiation at ¿2.4 GHz. The experiment showed that RF power systematically peaks at the time of the X-rays generation (in the measurement time scale). Sparks presents peaks of RF radiation before the breakdown of the gap. The peaks are related to the applied voltage to the gap. RF peaks are also detected in discharges without breakdown. Cases where X-rays are detected present higher RF peak power. The results indicate that at some stage of the discharge before the breakdown electrons are very fast accelerating letting in some cases to produce X-rays. Microwave radiation and X-rays may come from the same process.

RHESSI and AGILE TGFs distributions in the period 2009-2012 are compared. Analysis of differences in geographical, hourly, monthly distributions of the three main TGF production regions in Earth due to differences in lightning production and ITCZ movement is presented. A fourth region producing TGFs over Pacific not reported before is also analysed. Second analysis has been performed in order to identify preferable meteorological conditions for TGF production. Some publications suggested that regional differences in lightning/TGF ratio may be due to differences in meteorological thunderstorm and lightning production. All AGILE passes over South America (SA) in 2009-2012 has been studied. No special meteorological features characteristic of SA has been identified. TGFs are detected in situations with many lightning, thunderstorms, high CAPEs and high Top Clouds. TGFs are more probable to be detected in active situations.

Sprites and Elves are commonly observed in Europe, especially also in winter maritime storms. It is well known that sprites are related to large electric charge positive flashes and elves are related with high amplitude in either negative and positive flashes. The analysis of the occurrence of sprites and elves revealed that sprites can occur inland and over the sea whereas elves prefer to occur over the sea. The distribution of positive and negative flashes during the warm period (April-September) and the cold period (October-March) depicts that flashes with intense amplitudes present a particular pattern. Intense negative flashes occur mostly over the sea and coastal areas during summer and winter whereas intense positive tend to occur in the mountains during the warm season and over sea during the cold period. Also, sprite and elves can indicate regions where energetic flashes occur. This can be a valuable information related to the risk assesment of wind turbines.

On April 2015 a Lightning Mapping Array network (COL-LMA) was installed at the north of Colombia. This network provides 3D mapping of the development of lightning leaders. For the first time such network has been setup in the tropics. That allows us to investigate the high altitude development of lightning leaders. Here we present the results of the first measurements to confirm that negative leaders at altitudes of 15 km are common in the observed thunderstorms.

The paper presents winter lightning maps on specific regions in the northern hemisphere. Four different degrees of winter lightning activity are defined based on information derived from Japanese case. Based on this reference case it is possible to determine regions where winter lightning can be a threat to specific structures. Guidance on risk assessment to tall structures and wind turbines are described as well.

On 29-30 October 2013, a low-light video camera installed at Pic du Midi (2877m), recorded transient luminous events above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73°C, while its cloud to ground (CG) flash rate exceeded 30flmin-1. Some sprite events have long duration and resemble to dancing sprites. We analyze in detail the temporal evolution and estimated location of two series of sprite sequences, as well as the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies, and the current moment waveform of the lightning strokes. (i) In each series, successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region. (ii) The longer time-delayed (>20ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent strokes (