Scientific motivation

  BACKGROUND

    The problem of the thundercloud electrification and how lightning is initiated inside thunderclouds is one of the biggest unsolved problems in atmospheric sciences. The relationship between thundercloud electrification, lightning activity, wideband radio emission and particle fluxes have not been yet unambiguously established. One of most intriguing opportunities opening by observation of the high-energy processes in the atmosphere is their relation to lightning initiation. C.T.R. Wilson postulated acceleration of electrons in the strong electric fields inside thunderclouds in 1924.
   In 1992 Gurevich et al. developed the theory of the runaway breakdown, now mostly referred to as relativistic runaway electron avalanches - RREA. The separation of positive and negative charges in thundercloud and existence of a stable ambient population of the cosmic ray MeV electrons in the atmosphere enables acceleration of the electrons in direction of the Earth's surface (Thunderstorm ground enhancements, TGEs) and to open space (Terrestrial gamma flashes, TGFs). Thus both TGEs and TGFs precede the lightning activity and can be used for the research of poorly understood lightning initiation processes providing key research instrument – fluxes of electrons, neutrons and gamma rays originated in the thunderclouds. Information acquired from the time series of TGEs and TGFs along with widely used information on the temporal patterns of the radio waveforms will help to develop both reliable model of lightning initiation and detailed mechanism of electron acceleration in thunderclouds.

  Following topics will be covered during oral and poster sessions:     

• Research of the Thunderstorm ground enhancements (TGEs), measurements of electrons, gamma rays and neutrons by networks of particle detectors located on Earth’s surface;
• Research of the Terrestrial gamma-ray flashes (TGFs) observed by the orbiting gamma-ray observatories;
• Transient Luminous Effects of Thunderstorms and Lightning in the Upper Atmosphere
• Radio emissions produced by atmospheric discharges and particle fluxes; 
  
• Lightning initiation and its relation to the TGE and TGF;
• Large Extensive air showers and ambient population of the cosmic ray electrons –
  influence on lightning initiation and unleashing of the RREA;
• Neutron production during thunderstorms (lightning bolt or photonuclear reactions?)
• Ultraviolet and infrared emissions during thunderstorms;
  
• Monitoring of thunderclouds from orbit;  
  
• Monitoring of the thunderstorms by high speed cameras from the earths surface;
• Methods of the remote sensing of the thundercloud structure and electric field;   
• Relation of the lightning occurrences to the TGE and TGF initiation;   
• X-ray emissions from the lightning;   
• Relations to the climate and space weather issues;   
• Possibility of joint observations by space-born and ground-based facilities.