A global climatology of the mesospheric sodium layer from GOMOS data during the 2002–2008 period

This paper presents a climatology of the meso- spheric sodium layer built from the processing of 7 years of GOMOS data. With respect to preliminary results already published for the year 2003, a more careful analysis was applied to the averaging of occultations inside the climato- logical bins (10 in latitude-1 month). Also, the slant path absorption lines of the Na doublet around 589 nm shows evi- dence of partial saturation that was responsible for an under- estimation of the Na concentration in our previous results. The sodium climatology has been validated with respect to the Fort Collins lidar measurements and, to a lesser extent, to the OSIRIS 2003-2004 data. Despite the important nat- ural sodium variability, we have shown that the Na vertical column has a marked semi-annual oscillation at low latitudes that merges into an annual oscillation in the polar regions,a spatial distribution pattern that was unreported so far. The sodium layer seems to be clearly influenced by the meso- spheric global circulation and the altitude of the layer shows clear signs of subsidence during polar winter. The climatol- ogy has been parameterized by time-latitude robust fits to al-