On the Lightning Induced Transient Emissions (LITEs) in the OH Airglow Region with ISUAL Observations

Elves and sprites are the two recently observed lightning induced transient emissions (LITEs) in the mesosphere. Observations of elves by ISUAL broadband filter onboard the FORMOSAT-II satellite have sometimes shown a transient brightness at or below the OH airglow altitude in the event of a lightning flash. It is generally accepted that electrons heated by lightning EMPs impact N2 species to produce the optical emissions. Given that the sudden brightness oftentimes occurred at the OH airglow altitude and that OH species require only 3 to 4 eV to produce optical emissions, it is very possible that OH species can be another light-emitting species interacting with the EMP-accelerated electrons. Due to too much overlap of OH and N2 spectrum within the bandwidth of the broadband filter, it was not possible to determine which species are responsible for the observed enhancements. In response to the need to find the causes for such enhancements, ISUAL conducted a 9-day campaign in January 2007, with some observations devoted exclusively to capturing LITEs with the 630 nm filter for such an investigation. We will present the analysis of the observations from the CCD camera, spectrophotometer, and array photometer, and will discuss the implications of the results.