Global and seasonal variations in middle atmosphere CO from UARS/ISAMS

Carbon monoxide limb emissions at 4.6‐μm measured by the Improved Stratospheric And Mesospheric Sounder (ISAMS) on board the Upper Atmosphere Research Satellite (UARS) are presented. The main features observed in the radiance measurements are presented and discussed. These radiances are used to obtain the CO abundances in the middle atmosphere, using a special retrieval scheme which incorporates the non‐LTE nature of the CO emission at 4.6‐μm. The first global maps of the CO abundance in the middle atmosphere illustrating its latitudinal/seasonal variations are presented and briefly discussed. One of the most interesting results obtained is the increase in the CO relative abundance in the mesosphere towards the winter polar region, in accordance with previous predictions by 2D dynamical‐chemical models of the middle atmosphere.