Thermal structure of Venus nightside upper atmosphere measured by stellar occultations with SPICAV/Venus Express

The thermal structure of Venus upper atmosphere (90-140 km) was investigated using stellar occultation measurements acquired by the SPICAV experiment on board Venus Express. The SPICAV ultraviolet channel provides CO2 local density and temperature vertical profiles with a vertical resolution of <7km of both the southern and the northern hemispheres on the nightside (18:00-06:00 h local time). A permanent layer of warm air is observed at the mesopause in the altitude range 90-100 km. Temperature then decreases with increasing altitude reaching a minimum value around 125 km. Spatial and temporal changes in the thermal structure have been analyzed. Local time variations dominate the structure of Venus atmosphere at these altitudes: temperatures show an increase of ~20K on the morning side compared to the evening side. The homopause altitude was also determined; it varies between 119 and 138 km of altitude, increasing from the evening side to the morning side. SPICAV temperature profiles were compared to several literature results from ground-based observations, previous spacecraft missions and the Venus Express mission.