Corona UV signals observed under a thunderstorm on 27 June 2024. (a) Approximate location of all 859 corona UV signals observed during the ∼1.5-hr observation period on a sweetgum tree. Each corona UV signal is colored by the number of total isotropic UV photons between 255 and 273 nm emitted by the corona discharge, as estimated from the illuminated pixels observed in that frame. The boxes depict the Corona Observing Telescope System (COTS) UV camera field of view, and the colors indicate the observation time for the branch within each box. Panel (b) as in (a), but for all 93 corona UV signals observed during the ∼20-min observation period on a loblolly pine tree. Locations of boxes and corona UV signals are only approximate because the wind blew the branches in and out of the COTS field of view. Note a corona UV signal is defined as a contiguous bundle of several illuminated pixels.
