A global picture of the mesospheric sodium layer by the GOMOS instrument
Didier Fussen(1), Cédric Tétard(1), Filip Vanhellemont(1), Nina Mateshvili(1), Nicolas Loodts(1), Emmanuel Dekemeper(1), Christine Bingen(1), Nadège Capouillez(1), Erkki Kyrölä(2), Viktoria Sofieva(2), Johanna Tamminen(2), Alain Hauchecorne(3), Francis Dalaudier(3), Jean-Loup Bertaux(3), Odile Fanton d'Andon(4), Gilbert Barrot(4), Marielle Guirlet(4), Thorsten Fehr(5) and Lidia Saavedra(6)
(1) BIRA-IASB, 3,avenue Circulaire, B-1180 Brussels, Belgium
(2) FMI, Erik Palmenin aukio 1, 00101 Helsinki, Finland
(3) Service d'Aéronomie du CNRS - LATMOS, Bois de Verrieres, 91371 Verrieres le Buisson Cedex, France
(4) ACRI, route du Pin Montard, Sophia-Antipolis, France
(5) ESA, Via Galileo Galilei, Frascati, Italy
(6) ESA/ESRIN, , Frascati, Italy
7 years of GOMOS data have been processed in a statistical way in order to improve the signal-to-noise ratio of small absorbing constituents. A clear signature of the mesospheric sodium appears in the transmittance spectra. With respect to preliminary studies, we have now obtained the following results:
• The value of the D2/D1 ratio of the sodium doublet is mostly lower than 2 due to the partial saturation of the transition. Going from vertical columns (as used in lidar measurements) to slant path columns as measured from space induces not only an air mass factor but also a change in the absorption regime from linear to non-linear.
• The retrieved Na climatology shows a clear evidence of an annual cycle in the polar regions and a probable semi-annual cycle in the equatorial zone. Futhermore, mesospheric meridional transport can be easily tracked by the latitudinal dependence of the peak maximum.
• Despite the large natural variability of the Na sodium layer, we present a climatology that has been validated against ground-based lidar measurement. Special events are also discussed.