A 2-DIMENSIONAL MODEL OF RUNAWAY ELECTRON-BEAMS DRIVEN BY QUASI-ELECTROSTATIC THUNDERCLOUD FIELDS

Intense, transient quasi-electrostatic (QE) fields, which exist above thunderclouds following a positive cloud-to-ground lightning discharge , can produce an upward travelling runaway electron (REL) beam. A new two-dimensional (2D) REL-QE model is developed, expanding the previous ly reported 1D model [Bell et al., 1995] and incorporating the QE [Pas ko et al., 1997a] and the recently developed electrostatic heating (ES H) [Pasko et al., 1997b] models. The new model gives the lateral elect ron distribution in the beam and allows us to determine the ionospheri c effects and the optical luminosities resulting from the simultaneous action of the QE fields on the ambient electrons and the runaway elec trons. The mo del is self-consistent and includes the changes in space charge and conductivity due to the REL. Optical emissions and gamma-r ay emissions [Lehtinen et al., 1996a] are calculated and compared to e xperimental observations of Sprites and terrestrial gamma-ray flashes (TGF). It is shown that the structure of the electric field and the op tical emissions can be significantly affected by the REL.