József Bór

Gigantic jets produced by an isolated tropical thunderstorm near Réunion Island

Five gigantic jets (GJs) have been recorded with video and photograph cameras on 7 March 2010 above an isolated tropical storm east of Reunion Island. Three of them were produced before the storm reached its coldest cloud top temperature (approximately −81°C), and two others occurred during the cloud extension. Thanks to the close distance of observation (∼50 km), the luminosity within the cloud was recorded, and the events are analyzed in unprecedented detail. The tops of the GJs are estimated between 80 and 90 km. All these GJs are accompanied by long, continuous cloud illumination, and they are preceded and followed by intermittent optical flashes from the cloud, most of time without any cloud-to-ground (CG) flash simultaneously detected, which suggests they originated mainly as intracloud discharges and without any charge transfer to Earth. The CG lightning activity is observed to cease a few tens of seconds before the jets. According to ELF data recorded at Nagycenk, Hungary, the five GJs serve to raise negative charge. Their duration ranges from 333 to 850 ms. The leading jet has the most variable duration (33-167 ms) and propagates faster at higher altitudes. The trailing jet exhibits a continuous decrease of luminosity in different parts of the jet (lower channel, transition zone and, for most events, carrot sprite-like top) and in the cloud, with possible rebrightening. The lower channels (∼20-40 km altitude) produce blue luminosity which decreases with altitude and become more and more diffuse with time. The transition zone (around 40-65 km) consists of bright red, luminous beads slowly going up (∼104 m s−1), retracing the initial leading jet channels.

An unusual sequence of sprites followed by a secondary TLE: An analysis of ELF radio measurements and optical observations

We present an extraordinary case of sprites in rapid succession—four sprite clusters in only 400 ms—followed by a secondary jet. Simultaneous ELF and optical observations, as well as lightning data, enabled us to thoroughly document this unique event. Locations of the transient luminous events (TLEs) were triangulated using video recordings from Nydek (Czech Republic) and Sopron (Hungary). We found that sprites were displaced up to 70 km from their parent lightning. The current moment waveform and charge moment changes associated with the event were reconstructed from the ELF electromagnetic signature recorded at the Hylaty station (Poland) by a new method. The results suggest that both a short-delayed and a long-delayed sprite were generated by a single positive cloud-to-ground discharge that had an intense continuing current. It had an unusual progression and lasted 200 ms. A large increase in the current moment during the development of a massive carrot sprite provides evidence in favor of sprite current. Our results also support the formation of an electric environment hypothesized to be necessary for the generation of the secondary TLEs.

Observation of TLES in central europe from hungary supported by LINET

More than one hundred different transient luminous events (TLEs) i.e. sprites, sprite halos and one blue jet‐like emission have been observed in Central Europe at a new optical observation site in Sopron, Hungary, during the summer of 2007. The recently developed LINET lightning location network supplied information about the lightning activity in the region. This was the first time that data from this network was used to support TLE observations and to help interpret the results. TLE‐triggering lightning flashes were identified by their radiation in the ELF (Extremely Low Frequency) band, appearing as coherent transient signals with enhanced amplitudes in the monitored field components of the atmospheric electromagnetic field at NCK station in Hungary. Individual lightning flashes could be associated with 92% of the optically observed events. No ELF transient could be associated with the blue jet‐like emission, and for one sprite neither a corresponding transient nor any causative lightning flash could b...

Systematic deviations in source direction estimates of Q‐bursts recorded at Nagycenk, Hungary

Q-bursts are globally detectable extremely low frequency (ELF, 3-3000Hz) band wave packets produced by intense lightning discharges. Q-bursts recorded in the Szechenyi Istvan Geophysical Observatory (NCK, 16.7°E, 47.6°N), Hungary, on 1 and 2 August 2012 have been analyzed to find azimuths of their sources. The location of parent lightning strokes of 320 and 205 Q-bursts on the 2days, respectively, have been identified in the records of the World Wide Lightning Location Network (WWLLN) using the detection times at NCK. ELF data-based source azimuths were found to differ systematically from source azimuths obtained from WWLLN lightning locations. The difference between the corresponding azimuth values depends on the azimuth of the source. This variation of the source azimuth error mirrors the symmetry of the conductance of the Earths crust inferred from magnetotelluric measurements around NCK. After correction for the azimuthal dependence, the variation of the residual error shows a diurnal pattern with positive azimuth deviations occurring near midnight, local time. Fullekrug and Sukhorukov (1999) suggested that the anisotropic conductivity in the Earths crust below the observatory and the different daytime and nighttime conductivities in the lower ionosphere, respectively, may cause the identified error terms. Our results emphasize the substantial effect of anisotropic conductivity in the Earths crust around the recording station on the accuracy of ELF direction finding. The need for theoretical approach and more measurements is pointed in understanding the underlying mechanisms quantitatively and in investigating whether ELF observations can be used in geophysical prospecting.