GLOBAL AND SEASONAL-VARIATIONS IN MIDDLE ATMOSPHERE CO FROM UARS ISAMS

Carbon monoxide limb emissions at 4.6-mum measured by the Improved Str atospheric And Mesospheric Sounder (ISAMS) on board the Upper Atmosphe re Research Satellite (UARS) are presented. The main features observed in the radiance measurements are presented and discussed. These radia nces are used to obtain the CO abundances in the middle atmosphere, us ing a special retrieval scheme which incorporates the non-LTE nature o f the CO emission at 4.6-mum. The first global maps of the CO abundanc e in the middle atmosphere illustrating its latitudinal/seasonal varia tions 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 previou s predictions by 2D dynamical-chemical models of the middle atmosphere .