Observation of the chemiluminescent NO + O → NO2 + hν reaction in the upper mesospheric dark polar regions by OSIRIS on Odin

Abstract

The visible and near infrared continuum spectrum produced by the NO + O → NO2 + hv chemiluminescent reaction has been detected in the upper mesospheric dark polar regions by OSIRIS on the Odin spacecraft. Averaged observed NO2 emission spectral shapes are obtained by spectrally resolving the NO + O continuum from the blended strong upper mesospheric OH vibration–rotation airglow bands. The observed continuum spectral shape when compared with laboratory measurements is shifted to lower wavelengths by approximately 20 nm in the steeply sloped 400 to 500 nm region. The observed laboratory continuum spectral shape for upper mesospheric ambient pressure is presented for reference over the 400 to 800 nm region. An example of an NO2 continuum volume emission-rate altitude profile derived from a single OSIRIS limb scan is also included. Limb radiances up to 3 × 109 photons cm–2 nm–1 s–1 are observed at the peak of the NO2 continuum corresponding to total volume emission rates of approximately 2 × 104 photons cm–3 s–1. Data extracted from numerous single-volume emission-rate altitude profiles obtained over approximately a 24 h period are assembled into a Southern Hemisphere polar map of the 90 km NO2 continuum emission. The map illustrates the considerable spatial brightness variation typically observed in the dark Antarctic polar region throughout the OSIRIS mission dataset. After further analysis these measurements will assist in quantifying the role of thermospheric formed NOx in the catalytic removal of ozone in the upper stratosphere.