Summer high‐latitude mesospheric observations of supersonic bursts and O(1S) emission rate with the UARS WINDII instrument and the association with sprites, meteors, and lightning

Abstract

Supersonic neutral velocities, called supersonic bursts, are observed in localized regions lasting for over 8 s of enhanced O(1S) emission rate for tangent altitudes of 73–80 km during summer daytime by the Wind Imaging Interferometer (WINDII) on board the UARS satellite; the occurrence rate is 40% (≥500 m s−1) for latitudes above 65°N. These bursts are proposed to be produced by accelerated electrons and ions in a strong electric field. Theory suggests that an electric field of 45 V m−1 is required to generate a typical supersonic velocity of 750 m s−1 forced by ion‐neutral collisions at 82 km, the altitude at which polar mesospheric clouds occur. Coincidences in space and time between supersonic velocity profiles and space‐based lightning detection observed at a wavelength of 777.4 nm were found in a limited number of cases in high‐latitude summer, a region for which the lightning detection has the highest occurrence frequency (2–3.5%) and optical energy (1 J m−2 sr−1μm−1) as a function of month and latitude. The electric field must have sufficient energy to generate atomic emission features, more than for sprites and comparable with tropospheric lightning. Support for the existence of supersonic bursts at high latitude is provided through the observation of “chirps” in infrasound emissions which frequently occur in the absence of tropospheric lightning.