GAMMA RAY FLASHES DUE TO PLASMA PROCESSES IN THE ATMOSPHERE: ROLE OF WHISTLER WAVES

Whistler waves generated during a lightning play an important role in the generation of energetic electrons and their propagation to higher altitudes. The relativistic electrons produced by a cosmic ray shower during a thunderstorm can form the seed population that leads to a runaway discharge at an altitude of about 5 km. In such a discharge the energetic electrons ionize the neutral gas, thus producing thermal electrons which are accelerated to runaway energies by the thunderstorm electric field, and thus generating further ionization [1, 2]. Furthermore these relativistic electrons drive the whistler waves unstable and lead to the formation of ducts by the self-focusing as first suggested by Kaw et al.[3]. These ducts in turn facilitate the propagation of the energetic electrons to heights of about 30 km. At such altitudes the gamma rays produced by bremsstrahlung of the relativistic electrons can escape the atmosphere, and are well correlated with the gamma ray flashes detected by Compton Gamma Ray Observatory [4], and recently by the Reuven Ramaty High Energy Solar-Spectroscopic Imager (RHESSI) spacecraft. The focus of this paper is on the processes associated with the whistler waves excited by a beam of hot magnetized electrons in the atmosphere. We consider whistlers propagating in the two component plasma, which consists of a beam of relativistic runaway electrons and of cold electrons produced by the impact ionization of neutral gas (air). In this specific case the hot electron are magnetized, while the cold electrons are demagnetized due to electron-neutral collisions as it typical in the atmosphere from above 15 km and up to 70 km. The drift of the energetic electrons relative to the bulk electrons lead