Sprites triggered by negative lightning discharges

High altitude air breakdown, manifested as "red sprites," is reported in cl ose associated with negative cloud-to-ground lightning (-CG) on at least tw o occasions above an unusual storm on August 29, 1998. Data from high speed photometry, low-light-level video, and receivers of lightning electromagne tic signatures in the frequency range 10 Hz to 20 kHz are used to establish the association and indicate that the causative -CG discharges effected un usually large vertical charge moment changes (Delta M-Qv) of up to 1550 C.k m in 5 ms. The existence of sprites caused by -CG's, rather than the regula rly associated +CG's, has immediate implications for sprite models and obse rvations.