Universität zu Köln

Oschlisniok, Janusz (2020). Transport of sulfuric acid in the atmosphere of Venus studied on the basis of radio signal attenuation effects observed in the Venus Express Radio Science Experiment VeRa. PhD thesis, Universität zu Köln.

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Abstract

The most striking features on Venus are the cloud deck, which cover the entire planet at altitudes between about 50 and 70 km and its superrotating atmosphere. With highest zonal wind velocities in excess of 100 m/s at altitudes of about 65 to 70 km the atmosphere circles the planet in about four Earth-days. Until today, the mechanism that supports the superrotation is not understood. It is assumed that atmospheric waves, e.g. thermal tides, as well as meridional circulation may provide the required angular momentum. However, the knowledge about the meridional wind pattern is poor. The latter can be studied by means of their influence on the abundance and spatial distribution of trace gases like sulfuric acid and sulfur dioxide. The influence of atmospheric waves, on the other hand, can be seen for example in temporal temperature and density variations of the trace gases. While increased abundances of SO2 exist at altitudes below about 60 km altitude, significant amounts of H2SO4(g) can be found in the altitude region below about 50 km altitude. H2SO4 is produced in the upper clouds (60 - 70 km) where it predominantly exists in the liquid phase. It is transported to lower altitudes where it evaporates due to increasing temperatures so that a haze layer consisting of H2SO4(g) is formed between about 35 and 50 km altitude. Gaseous sulfuric acid and sulfur dioxide are responsible for the absorption of radio waves. The absorption can be used to derive the abundances of SO2 and H2SO4(g). The radio science experiment VeRa on board the Venus Express spacecraft was used to sound the atmosphere of Venus with X- and S-band radio waves between the years 2006 and 2014. In the present work, X- and S-band absorptivity profiles were derived from these radio soundings. Those were used to derive mean SO2 values between 51 and 54 km altitude as well as H2SO4(g) abundance profiles between about 40 and 55 km altitude. More than 800 profiles could be derived which, thanks to the orbit of Venus Express, cover a large number of latitudes and local times. Distinct latitudinal variations of SO2 and H2SO4(g) were found. Mean SO2 values of 90 ppm and 150 - 160 ppm were derived at the equatorial and the polar regions, respectively, while a relatively low mean abundance value of 50 ppm was found at the mid-latitudes. Increased H2SO4(g) accumulations with mean values of 13 ppm and 9 - 14 ppm were observed at low and high latitudes, respectively, while lower values of 5 - 7 ppm were derived at the mid-latitudes. Furthermore, a decrease of the topside of the H2SO4(g) haze layer was observed at higher latitudes. Long-term variations of SO2 were found at both polar regions with SO2 low abundant periods in the years 2006/2007 and 2013 as well as with an SO2 high abundant period between the years 2008 and 2011. A similar long-term trend was observed in the H2SO4(g) abundance at the northern polar latitudes. Lowest values were observed in 2007, while distinctly enhanced values were found between the end of 2008 and middle of 2012. Moreover, a local time dependence was found in the equatorial H2SO4(g) abundance, which is likely caused by a semidiurnal tide. A 2D mass transport model was developed in the present work in order to study the meridional wind pattern in Venus' atmosphere which caused the observed spatial distribution of H2SO4(g). It turned out that the H2SO4(g) accumulation observed at high latitudes was mainly caused by precipitation of H2SO4 droplets at these latitudes. The latter evaporated into gaseous sulfuric acid at lower altitudes and formed the observed gas accumulation. The influence of wind transport on this formation process was minor. The H2SO4(g) accumulation observed at equatorial latitudes is the result of opposite directed mass transport by upward winds and sedimentation as well as evaporation and condensation processes. The low H2SO4(g) abundance observed at mid-latitudes was reproduced by downward winds in the model calculations. The general assumption on Venus' wind pattern made in the present model is confirmed by the successful reproduction of the observed global H2SO4(g) distribution. The assumed wind pattern is also supported by the latitudinal SO2 distribution observed between 51 and 54 km altitude.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Oschlisniok, Janusz joschlis@uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-207503
Date:	10 August 2020
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Externe Einrichtungen > An-Institute > Associated Institutes of the Faculty of Mathematics and Natural Sciences > Rhenish Institute for Environmental Research - RIU
Subjects:	Physics Earth sciences
Uncontrolled Keywords:	Keywords Language Radio Science, Radio Occultation, Venus Express, Venus, Absorption, Clouds, Sulfuric Acid, Sulfur Dioxide, Atmospheric Dynamics English
Date of oral exam:	6 October 2020
Referee:	Name Academic Title Pätzold, Martin Priv. Doz. Dr. Eckart, Andreas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/20750