Identification of the aurorals O(¹S) precursor in photometric time sequences of pulsating aurora

Previous studies of photometric time sequences from pulsating aurora have established that the O({sup 1}S) metastable leading to the emission of the auroral green line is excited by two processes, one direct, the other indirect, with the indirect precursor having a lifetime of about 0.1s. In this paper the authors report on new high time-resolution measurements which extend the observations of precursor lifetime down to about 0.01s. Simultaneous observations of pulsations in the Begard-Kaplan band system were also made in order to obtain direct measurements of the lifetimes of the N{sub 2}(A{sup 3}{Sigma}{sub u}{sup +}) metastable; there were found to be essentially equal to those of the precursor over the lifetime range from 0.01s to 0.1s, and less well-correlated for longer lifetimes. This result identifies the O({sup 1}S) precursor as N{sub 2}(A{sup 3}{Sigma}{sub u}{sup +}), at least over the altitude range 97 to 125 km.