Ozone vertical distribution in Mars Years 27–30 from SPICAM/MEX UV occultations

Abstract

The 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 good spatial and seasonal coverages. We have analyzed these occultations and performed a rigorous quality check of the retrievals to eliminate false detections. We present the observed features of the vertical distribution of Martian ozone, a key chemical species. Stellar occultations probe the nightside atmosphere, whereas solar occultations are acquired at the terminator (sunrise or sunset), enabling 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 agreement. However, quantitative differences are found in certain regions, possibly related to difficulties in correct modeling of the water cycle. Our dataset allows us to study certain particular features of Martian ozone. The low- and midlatitude ozone layer forming during northern spring is mapped in both hemispheres and its night–terminator variations are probed with the combination of stellar and solar occultations. The southern polar winter vortex shows hints of the well-known mid-altitude ozone layer already detected previously. During the northern polar spring, SPICAM observes the top of the lower atmosphere ozone layer above 10 km, showing O3 concentrations that the model reproduces quite well. SPICAM observations are in good agreement with previously published observations from other instruments.