Climatology of the ozone vertical distribution on Mars from SPICAM/MEX UV occultations

International audienceThe SPICAM/MEX ultraviolet spectrometer probed the Martian atmosphere with the occultation method from 2004 until 2014. SPICAM/MEX performed both stellar and solar occultations during in total four Martian Years with a good spatial and seasonal coverages. We have analyzed these occultations and compiled a climatology of the vertical distribution of Martian ozone, a key chemical species. The stellar occultations mostly probe the nightside atmosphere, whereas the solar occultations are acquired at the terminator (sunrise or sunset), allowing the study of the day-night transition of this photochemically active species. Comparison of the observations with a global climate model show a good overall qualitative agreement. However, quantitative differences are found in certain regions, possibly related to difficulties in correct modeling of the water cycle. In particular, at low latitudes SPICAM is detecting ozone practically throughout the Martian Year, whereas it is only predicted around aphelion in the models. The occultations probe the southern polar winter vortex, its mid-altitude ozone layer (peaking at 50 km), and the ozone layer in the lower atmosphere that shows much larger O3 column concentrations than predicted by modeling. The low- and midlatitude ozone layer forming in northern spring is mapped throughout both hemispheres and details of its structure are revealed. During the northern polar spring, SPICAM observes the lower atmosphere ozone layer, reaching from the surface up to 30 km, showing higher O3 concentrations than expected from modeling