LOGARITHMIC DECAY AND DOPPLER-SHIFT OF PLASMA ASSOCIATED WITH SPRITES

VLF phase and amplitude perturbations in 'early/fast Trimpis' have bee n observed simultaneously on two or more transmitters at two or more r eceiver sites and simultaneously with sprites observed optically in Co lorado. In all cases the early/fast Trimpis could apparently be resolv ed into two components: the RORD (rapid onset, rapid decay) component coincident with the sprite and a 'classic Trimpi' component having the slower onset and decay of Trimpis generally thought to be caused by w histler-induced electron precipitation from the radiation belts. The p hase and amplitude perturbations can decay at very different rates, an d even change in sign from positive to negative perturbation ('oversho ot') during decay. This implies a spatial separation between the rapid decay plasma responsible for the RORD and the slow decay plasma respo nsible for the classic 'Trimpi component of up to a few tens of km. Th is is much less than the expected separation of sprite plasma and elec tron precipitation plasma induced by the same cloud-ground lightning. The discovery of very strong early/fast Trimpis in the tropics (Darwin , Australia), where electron precipitation is unlikely, which showed s imilar effects like overshoot but much more clearly, caused an examina tion of recent Colorado data of high resolution. The Colorado Trimpis, which are clearly associated with sprites, show the same features as the Darwin Trimpis where optically detected sprites were not available . Both can be explained in terms of sprite plasma decaying from the bo ttom up without recourse to electron precipitation. (C) 1998 Elsevier Science Ltd. All rights reserved.