Nitric oxide in the polar mesosphere-lower thermosphere: comparisons between OSIRIS, SMR, and ACE-FTS satellite measurements

There are very few satellite missions that derive polar nighttime nitric oxide (NO) concentrations in the upper atmosphere. From observations of the NO + O (+ M) → NO₂ (+ M) continuum, the Optical Spectrograph and InfraRed Imaging System (OSIRIS) on board the Odin satellite has recently retrieved an eight-year dataset of nighttime NO densities. The dataset shows that polar NO concentrations are dependent on the solar cycle and are currently increasing due to increasing geomagnetic activity. As well, around winter solstice OSIRIS NO densities typically peak at a height near 95 km, roughly 11 km lower than the currently accepted peak height. This study discusses the results of comparisons between the OSIRIS dataset, the co-located NO measurements retrieved by the Sub-Millimetre Radiometer (SMR) also on board Odin, and twilight NO mixing ratios derived from the Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) on board SCISAT.