Physical mechanisms for the development of lightning discharges between a thundercloud and the ionosphere

An investigation is made of the influence of changes in atmospheric pressur e with altitude and the thundercloud geometry on the development of lightni ng propagating upward to the ionosphere. It is shown that the mechanism for the development of high-altitude lightning does not differ from that for t he formation and propagation of ordinary lightning between a thundercloud a nd the ground. It is established that high-altitude lightning forms as a re sult of a reduction in pressure with altitude and can only take place from thunderclouds located at high altitudes. (C) 1999 American Institute of Phy sics. [S1063-7842(99)02804-4].