First mesopause Na retrievals from satellite Na D-line nightglow observations†

We report the retrieval of Na concentration profiles in the mesopause region from satellite observations of the Na D-line nightglow emission near 589 nm made by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) on the Envisat spacecraft. The retrieval assumes the Na D-line excitation mechanism originally proposed by Chapman in 1939. The retrieval approach, including treatment of self-absorption by Na, a retrieval uncertainty budget, and first retrieval results, is presented. The retrieved Na profiles are compared to independent satellite measurements. Good agreement in terms of peak altitude, peak concentration, and vertical column density is found. The retrievals constitute the first Na profile retrievals from satellite observations of the Na D-line nightglow emission profile. They enable our understanding of the Na nightglow excitation mechanism to be tested.