Diurnal variability of vibrationally excited mesospheric ozone as observed during the SPIRE Mission

Abstract

Spectrally resolved observations of infrared fluorescence (9–12 µm) from mesospheric ozone in the earth limb have been analyzed to deduce local excited vibrational state number densities as functions of altitude and solar illumination between 70 and 105 km. The nighttime and insolated quiescent polar atmospheres were sampled near the dawn terminator by a rocket‐borne cryogenic scanning filter spectrometer. Both the total intensity and the spectral distribution of the ozone fluorescence were observed to change after sunrise. The deduced vibrational populations revealed that this change was primarily due to a daytime reduction in the population of O3 (υ = 1), which is excited directly from ground state O3 by resonance absorption of earth radiation. In contrast, higher vibrational levels, formed by three‐body recombination of O and O2, show diurnal variations only at the lower altitudes, where the atomic oxygen concentration is expected to increase upon insolation. Thus the O3 (υ) fluorescence appears to be closely coupled to the local photochemical behavior of O and O3 near the mesopause.