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 Széchenyi István 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 Earth's 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. Füllekrug and Sukhorukov (1999) suggested that the anisotropic conductivity in the Earth's 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 Earth's 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. © 2016. American Geophysical Union. All Rights Reserved

Ground-based observations of the relations between lightning charge-moment-change and the physical and optical properties of column sprites

Optical observations of 66 sprites, using a calibrated commercial CCD camera, were conducted in 2009-2010 and 2010-2011 winter seasons as part of the ILAN (Imaging of Lightning And Nocturnal flashes) campaign in the vicinity of Israel and the eastern Mediterranean. We looked for correlations between the properties of parent lightning (specifically, the charge moment change; CMC) to the properties of column sprites, such as the measured radiance, the length and the number of column elements in each sprite event. The brightness of sprites positively correlates with the CMC (0.7) and so does the length of sprite elements (0.83). These results are in agreement with previous studies, and support the QE model of sprite generation. © 2013 Elsevier Ltd

Searching for effects caused by thunderstorms in midlatitude sporadic E layers

Possible thunderstorm - sporadic E (Es) layer coupling effects are investigated during two measurement periods, one in 2013 and one in 2014. The analysis was based on ionospheric observations obtained from a Digisonde at Pruhonice, the Czech Republic, an ionosonde at Nagycenk, Hungary, and a 3.59 MHz five-point continuous HF Doppler system located in the western part of the Czech Republic. The latter is capable of detecting ionospheric wave-like variations caused by neutral atmospheric waves generated by thunderstorms. The present study searches for possible impacts on Es layers caused by the presence of two active thunderstorms: one passing across the Czech Republic on June 20, 2013 (19:00 - 01:00 LT), and one through Hungary on July 30, 2014 (11:00 - 01:00 LT). During these two time periods, presence and parameters of Es layer were inferred from ionograms, recorded every minute at Pruhonice and every two minutes at Nagycenk, whereas concurrent lightning activity was monitored by the LINET detection network. In addition, transient luminous events (TLEs) were also observed during both nights from Sopron, Hungary and from Nydek, the Czech Republic. A noticeable fact was the reduction and disappearance of the ongoing Es layer activity during part of the time in both of the traversing thunderstorms. The analysis indicated that the critical frequency foEs dropped below ionosonde detection levels in both cases, possibly because of thunderstorm activity effects. This option, however, needs more case studies in order to be further substantiated

Multi-instrumental analysis of large sprite events and their producing storm in southern France

During the night of 01-02 September, 2009, seventeen distinct sprite events including 3 halos were observed above a storm in north-western Mediterranean Sea, with a video camera at Pic du Midi (42.93N; 0.14E; 2877m). The sprites occurred at distances between 280 and 390km which are estimated based on their parent CG location. The MCS-type storm was characterized by a trailing-stratiform structure and a very circular shape with a size of about 70,000km2 (cloud top temperature lower than -35°C) when the TLEs were observed. The cloud to ground (CG) flash rate was large (45min-1) one hour before the TLE observation and very low (<5min-1) during it. Out of the 17 sprite events, 15 parent+CG (P+CG) strokes have been identified and their average peak current is 87kA (67kA for the 14 events without halo), while the associated charge moment changes (CMC) that could be determined, range from 424 to 2088±20%Ckm. Several 2-second videos contain multiple sprite events: one with four events, one with three events and three with two events. Column and carrot type sprites are identified, either together or separately. All P+CG strokes are clearly located within the stratiform region of the storm and the second P+CG stroke of a multiple event is back within the stratiform region. Groups of large and bright carrots reach ~70km height and ~80km horizontal extent. These groups are associated with a second pulse of electric field radiation in the ELF range which occurs ~5ms after the P+CG stroke and exhibits the same polarity, which is evidence for current in the sprite body. VLF perturbations associated with the sprite events were recorded with a station in Algiers. © 2012 Elsevier B.V