Potential vorticity of the south polar vortex of Venus

©2016. American Geophysical UnionVenus' atmosphere shows highly variable warm vortices over both of the planet's poles. The nature of the mechanism behind their formation and properties is still unknown. Potential vorticity is a conserved quantity when advective processes dominate over friction and diabatic heating and is a quantity frequently used to model balanced flows. As a step toward understanding the vortices' dynamics, we present maps of Ertel's potential vorticity (EPV) at Venus' south polar region. We analyze three configurations of the south polar vortex at the upper cloud level (P ~ 240 mbar; z ~ 58 km), based on our previous analyses of cloud motions and thermal structure from data acquired by the Visual and InfraRed Thermal Imaging Spectrometer instrument on board Venus Express. Additionally, we tentatively estimate EPV at the lower cloud level (P ~ 2200 mbar; z ~ 43 km), based on our previous wind measurements and on static stability data from Pioneer Venus and the Venus International Reference Atmosphere (VIRA) model. Values of EPV are on the order of 10−6 and 10−8 K m2 kg−1 s−1 at the upper and lower cloud levels, respectively, being 3 times larger than the estimated errors. The morphology observed in EPV maps is mainly determined by the structures of the vertical component of the relative vorticity. This is in contrast to the vortex's morphology observed in 3.8 or 5 µm images which are related to the thermal structure of the atmosphere at the cloud top. Some of the EPV maps point to a weak ringed structure in the upper cloud, while a more homogenous EPV field is found in the lower cloud

Validation of the IPSL Venus GCM Thermal Structure with Venus Express Data

General circulation models (GCMs) are valuable instruments to understand the most peculiar features in the atmospheres of planets and the mechanisms behind their dynamics. Venus makes no exception and it has been extensively studied thanks to GCMs. Here we validate the current version of the Institut Pierre Simon Laplace (IPSL) Venus GCM, by means of a comparison between the modelled temperature field and that obtained from data by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) and the Venus Express Radio Science Experiment (VeRa) onboard Venus Express. The modelled thermal structure displays an overall good agreement with data, and the cold collar is successfully reproduced at latitudes higher than +/−55°, with an extent and a behavior close to the observed ones. Thermal tides developing in the model appear to be consistent in phase and amplitude with data: diurnal tide dominates at altitudes above 102 Pa pressure level and at high-latitudes, while semidiurnal tide dominates between 102 and 104 Pa, from low to mid-latitudes. The main difference revealed by our analysis is located poleward of 50°, where the model is affected by a second temperature inversion arising at 103 Pa. This second inversion, possibly related to the adopted aerosols distribution, is not observed in data

Latitudinal Variation of Clouds’ Structure Responsible for Venus’ Cold Collar

International audienceGlobal Climate Models (GCM) are very useful tools to study theoretically the general dynamics and specific phenomena in planetary atmospheres. In the case of Venus, several GCMs succeeded in reproducing the atmosphere’s superrotation and the global temperature field. However, the highly variable polar temperature and the permanent cold collar present at latitude have not been reproduced satisfactorily yet

Validation of the IPSL Venus GCM thermal structure with VIRTIS data

International audienceThe understanding of the mechanisms behind the planetary atmospheres along with their dynamics and structure, relies on General Circulation Models (GCMs). Here we compare the thermal structure from the latest version of the LMDZ Venus GCM developed at the Laboratoire de Météorologie Dynamique of Paris, against the one retrieved by VIRTIS, the Imaging Spectrometer flown on board the ESA Venus Express mission

Investigations below the clouds of Venus with the IPSL Venus GCM

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Status of the IPSL Venus global climate model

International audienceBased on our experience of Earth and Mars Global Climate Models, a model for Venus's climate system has been developed within Institute Pierre Simon Laplace (LMD, LATMOS) for twelve years. Thermal radiation scheme is based on Net-Exchange Rate (NER) matrices, with look-up tables for solar heating rate forcing

Evaluation of new radio occultation observations among small satellites at Venus by data assimilation

International audienceWe conducted observing system simulation experiments (OSSEs) for radio occultation measurements (RO) among small satellites, which are expected to be useful for future Venus missions. The effectiveness of the observations based on realistic orbit calculations was evaluated by reproduction of the "cold collar", a unique thermal structure in the polar atmosphere of Venus. Pseudo-temperature observations for the OSSEs were provided from the Venus atmospheric GCM in which the cold collar was reproduced by the thermal forcing. The vertical temperature distributions between 40 and 90 km altitudes at observation points were assimilated. The result showed that the cold collar was most clearly reproduced in the case where the temperature field in high-latitudes was observed twice a day, suggesting that the proposed observation is quite effective to improve the polar atmospheric structure at least. Although the cold collar was also reproduced in the OSSEs for Longwave Infrared Camera (LIR) observations, the result seemed unrealistic and inefficient compared to that obtained in the RO OSSEs. The present study shows that the OSSEs can be used to evaluate observation plans and instruments in terms of reproducibility of specific atmospheric phenomena, and applied to future missions targeting planetary atmospheres

Observing system simulation experiment for radio occultation by small satellites of the Venus atmosphere

International audienceUsefulness of radio occultation measurement by small satellites is investigated by observing system simulation experiment (OSSE) of the Venus data assimilation system. Idealized observations are prepared by French Venus Atmospheric GCM (LMD/VGCM) in which cold collar is realistically reproduced. The reproducibility of cold collar is tested by several types of observations. Results show that cold collar is successfully reproduced at least 6 hourly 3 vertical temperature profiles in the polar region. Therefore, radio occultation measurement by three satellites in polar orbits would be promising to reproduce cold collar

The study on the reproducibility of cold collar assuming radio occultation measurement by small satellites

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