RESEARCH
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The puzzling transition region of Venus atmosphere studied by a ground-to-thermosphere 3D model

G. Gilli, S. Lebonnois, P. Machado, R. Gonçalves

Abstract
The middle/upper atmosphere of Venus, notably between 70 and 120 km, is the so-called “transition region” between the retrograde superrotating zonal flow dominating below 65 km, and the day-to-night circulation created by inhomogeneous heating by solar radiation above 120 km. Venus Express observations (2006-2014) showed that this region is more variable than expected, with latitude and day-to-day variations of temperature up to 80 K above 100 km at the terminator (Mahieux et al. 2015), and apparent zonal wind velocities measured around 96 km on the Venus nightime, highly changing in space and time (Soret et al. 2014). Those variations are not fully explained by current 3D models and specific processes (e.g. GW propagation, thermal tides, large scale planetary waves) responsible for driving them are still under investigation.We propose here to use the current improved version of the LMD Venus General Circulation Models (VGCM) (Lebonnois et al. 2016, Gilli et al. 2017) to yield insight into the global circulation of this region by fostering data-model synergies. Zonal wind predictions above 60 km by our VGCM showed to be consistent with available measurements (Peralta et al. 2017). On-going ground-based Venus observation on the cloud tops (~70 km) and below (Machado et al. 2017) will add complementary information to understand the coupling between the lower and upper atmosphere of Venus. In addition, observed O2(1∆) nightglow, CO and O density (Gilli et al. 2015, Vandaele et al. 2016, Gerard et al. 2009), usually considered as sensitive transport tracers in the upper atmosphere of Venus where no direct wind measurements are available, will be interpret with the help of 3D model results.

BAAS

American Astronomical Society
Volume 49, Number 5
2017 October

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia