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Sprites are optical emissions in the mesosphere mainly at altitudes 50-90 km. They are caused by the sudden re-distribution of charge due to lightning in the troposphere which can produce electric fields in the mesosphere in excess of the local breakdown field. The resulting optical displays can be spectacular and this has led to research into the physics and chemistry involved. Imaging at faster than 5,000 frames per second has revealed streamer discharges to be an important and very dynamic part of sprites, and this paper will review high-speed observations of sprite streamers. Streamers are initiated in the 65-85 km altitude range and observed to propagate both down and up at velocities normally in the 10-5 × 10 m/s range. Sprite streamer heads are small, typically less than a few hundreds of meters, but very bright and appear in images much like stars with signals up to that expected of a magnitude −6 star. Many details of streamer formation have been modeled and successfully compared with observations. Streamers frequently split into multiple sub-streamers. The splitting is very fast. To resolve details will require framing rates higher than the maximum 32,000 fps used so far. Sprite streamers are similar to streamers observed in the laboratory and, although many features appear to obey simple scaling laws, recent work indicates that there are limits to the scaling. [ABSTRACT FROM AUTHOR]

This paper presents a literature survey on the recent developments related to modeling studies of transient luminous events termed sprites and sprite halos that are produced at mesospheric and lower ionospheric altitudes in the Earth's atmosphere by lightning. The primary emphasis is placed on publications that appeared in the refereed literature starting from year 2010 and up to the present date. The survey focuses on the interpretation of morphological features observed in sprites. We introduce parameters typically used for quantitative description of electron avalanches and discuss the importance of space charge effects on different spatial scales, including sprite halos (exhibiting 10s of km transverse extents) and sprite streamers (requiring submeter resolution for accurate description). A special emphasis is placed on the interpretation of initiation and development of sprite streamers captured in high-speed video observations and a critical review of the most recent modeling efforts related to these observations. We also discuss fundamental reasons for polarity asymmetry in existing sprite observations indicating that vast majority of sprites with well-developed streamer structure are produced by positive cloud-to-ground lightning discharges. [ABSTRACT FROM AUTHOR]

This paper gives a resume of the papers written in English which (a) describe some of the recording instruments in use at the Nagycenk Observatory (NCK) since the International Geophysical Year (IGY 1957-1958) and up to the present time, (b) summarise the most important and different types of observations associated with thunderstorms which have been made there, and (c) discuss their various geophysical interpretations. The paper describes the main results which have been obtained in four areas of thunderstorm associated atmospheric and geospace science within the context of Earth system science. These relate to the following parameters of atmospheric electricity: the vertical electric potential gradient just above the Earth's surface and the air-Earth current as well as the point discharge current, Schumann resonance (SR) signals of the Earth-ionosphere cavity at 8, 14 and 20 Hz, transient luminous events (TLEs), and some aspects of the behaviour of the ionosphere. Deductions from these data sets are concerned with the global lightning activity and the conductivity of the air, with diurnal, seasonal, annual and long-term variations of the SR amplitudes and resonant frequencies in terms of migrating thunderstorm centres, with transient SR excitations and with sprites and other TLEs, and with ionospheric disturbances. The paper closes with some thoughts on future research directions based on the observations at NCK and Sopron and the results achieved since the IGY. [ABSTRACT FROM AUTHOR]