A multiple-fluid, quasi-electrostatic simulation model is used to examine the effects of lightning on the atmosphere between 20 km and 90 km altitude. Two principal new results are obtained. (1) First, significant space charge is found in the altitude range 20 to 40 km during a positive, but not negative, cloud-to-ground (CG) discharge. (2) Second, a lightning flash is shown to increase total conductivity in the altitude range of 20 to 40 km by at least an order of magnitude, 10 s after the discharge. This is due to the lingering effects of the ion and electron redistribution caused by the lightning discharge. ¿ 1998 American Geophysical Union