The thermal structure of the Venus atmosphere: Intercomparison of Venus Express and ground based observations of vertical temperature and density profiles

Abstract

Highlights  The Venus International Reference Atmosphere (VIRA) model developed from results of the Venera and Pioneer Venus Orbiter and Multi-Probe missions in early 1980s has been very useful in Venus atmospheric studies for the last several decades. The recent long term monitoring of the Venus atmosphere from Venus Express mission has added a lot of new information about the atmospheric structure above about 40 km altitude and up to nearly 200 km from passive infrared remote sensing, occultation at radio, infrared and ultraviolet wavelengths and in-situ atmospheric drag data from the orbiter. New results from ground based measurements have also provided new information. This paper examines these new results to evaluate the agreements and disagreements between them as a step towards updating the VIRA model. Despite the different techniques, spatial resolutions and temporal coverage, a consistent picture of the thermal structure emerges and shows considerable variability above 100 km, and presence of warm and cold layers not characterized before. Some differences in the density profiles from the three occultation experiments where their respective altitude coverage ranges are nearly overlap. Abstract The Venus International Reference Atmosphere (VIRA) model contains tabulated values of temperature and number densities obtained by the experiments on the Venera entry probes, Pioneer Venus Orbiter and multi-probe missions in the 1980s. The instruments on the recent Venus Express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the Venus atmosphere from 40 km to about 180 km altitude from April 2006 to November 2014. Many ground based experiments have provided data on the upper atmosphere (90-130 km) temperature structure since the publication of VIRA in 1985. The "Thermal Structure of the Venus Atmosphere" Team was supported by the International Space Studies Institute (ISSI), Bern, Switzerland, from 2013 to 2015 in order to combine and compare the ground-based observations and the VEx observations of the thermal structure as a first step towards generating an updated VIRA model. Results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry. The intercomparison of the ground-based and VEx results provides for the first time a consistent picture of the temperature and density structure in the 40 km -180 km altitude range. The Venus Express observations have considerably increased our knowledge of the Venus atmospheric thermal structure above ~40 km and provided new information above 100 km. There are, however, still observational gaps in latitude and local time above certain regions. Considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present, such as a succession of warm and cool layers. Preliminary modeling studies support the existence of such layers in agreement with a global scale circulation. The intercompar...

Stationary Features at the Cloud Top of Venus Observed by Ultraviolet Imager Onboard Akatsuki

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Morphology and Dynamics of Venus's Middle Clouds With Akatsuki/IR1

“…Such strong hemispherical asymmetries have never been reported on the UV albedo, and their cause is yet to be determined although inhomogeneities in the distribution of an absorber at NIR wavelengths (Titov et al, 2012) cannot be ruled out. The sharp albedo changes displayed in Figure 1c have never been observed before Akatsuki (Limaye et al, 2017), and they were recurrent during the first half of 2016 and absent on UV images of the upper clouds. They involve a 1-4% decrease in the photometrically corrected radiance and, since they moved with zonal speeds ∼10-20 m/s faster than other cloud features, we interpret them as atmospheric waves.…”

Initial performance of the radio occultation experiment in the Venus orbiter mission Akatsuki

“…The region above 58 km is also stable and is dominated by short-vertical scale (< 5 km) fluctuations, being consistent with Venus Express radio occultation experiments . The range of the temperature variation near the top is ~ 50 K, which is smaller than the day-to-day variability of ~ 80 K in the same height region observed by the solar occultation experiment SOIR onboard Venus Express (Mahieux et al 2012;Limaye et al 2017). More measurements are needed to better understand the variability.…”