THE POSITIVE CHARGE RESERVOIR FOR SPRITE-PRODUCING LIGHTNING

The close association of mesospheric sprites with positive ground flas hes has led to the frequent assumption that positive charge is transfe rred from the top of a thunderstorm with positive-over-negative charge structure, from an altitude of 10 km or higher. Electrical and meteor ological observations are reviewed which support a different picture: sprites are produced by laterally extensive mesoscale convective syste ms (MCS) in which the positive charge reservoir predominates in the 4- 6 km ranges of altitude. The behavior of the surface electric field du ring the End-of-Storm Oscillation and the behavior of the vertical ele ctric held above MCS during positive ground flashes both suggest a pre dominant in-cloud dipole moment with opposite polarity to that of the ordinary thundercloud. Lightning charge transfers of a few hundred Cou lombs from the 4-6 km height range may be required for consistency wit h theories for sprite optical intensity and to account for ELF Q-burst intensity. (C) 1998 Elsevier Science Ltd. All rights reserved.