Séminaire LATMOS (Amphithéâtre Gérard Mégie, Guyancourt), Jeudi 18 septembre 2014, 11h

Orateur: Arianna Piccialli (LATMOS)

Titre:Thermal structure of Venus’ nightside upper atmosphere measured by SPICAV UV on Venus Express"

Venus upper atmosphere (70 – 150 km altitude) is one of the most intriguing regions on the planet. It corresponds to a transition region characterized by a complex dynamics: strong retrograde zonal winds dominate the lower mesosphere while a solar-to-antisolar circulation driven by a day-to-night temperature gradient can be observed in the upper mesosphere/lower thermosphere (Schubert et al., 2007). The thermal structure of Venus upper atmosphere shows a significant variability both on day-to-day as well as longer timescales (Clancy et al., 2012; Sonnabend et al., 2012).

The SPICAV (Spectroscopy for the investigation of the characteristics of the atmosphere of Venus) instrument has been operating on board the ESA orbiting platform Venus Express since 2006. In the stellar occultation mode the ultraviolet channel provides CO2 local density and temperature vertical profiles with a vertical resolution of < 7 km of both the Southern and the Northern hemispheres on the night side (6 pm to 6 am local time).

I will present the thermal structure of Venus upper atmosphere based on SPICAV-UV measurements. A permanent warm area appears distinctly at the mesopause at about 90 – 100 km of altitude (Bertaux et al., 2007; Rengel et al., 2008;  Mahieux et al., 2012); the temperature then decreases with increasing altitude reaching a minimum value around 125 km. We analyzed spatial and temporal changes in the thermal structure. Local time variations dominate the structure of Venus atmosphere at these altitudes: temperatures show an increase of about 20 K on the morning side compared to the evening side. The homopause altitude is also determined; it varies between 119 and 138 km of altitude, showing no dependence on the latitude or local time.