The circulation in the troposphere of Venus follows an almost purely zonal flow, with windspeeds of about 100 m/sec at 60-70 km altitude, which corresponds to the upper cloud deck. These winds quickly decrease from mid to higher latitudes, eventually reaching zero at the poles, and also from midlatitudes towards the equator they get slower.
The winds have also a strong vertical gradiënt, declining deep in the troposphere with the rate of 3 m/sec per km.

Venus circulation Author of the image: RuslicO

It is licensed under the Creative Commons Attribution Share Alike 3.0 Unported license.

But there's also the so called Hadley circulation with hot air rising in the equatorial zone and flowing to the poles, and these meridional air motions are much slower than the zonal winds.

This dissertation at page 14, describes a cycle of the making and decomposing of sulfuric acid within this meridional circulation.

From the lower atmosphere, SO$_2$ is transported upward and becomes the source for H$_2$SO$_4$, mostly produced in a thin layer of about 2 km depth near the cloud top. With the SO$_2$, oxygen atoms there, produced by UV radiation of CO$_2$, form SO$_3$ that combines with water vapour to yield the H$_2$SO$_4$.

Within the circulation the sulfuric acid is transported towards the 60$^0$ latitudes where it descends to the lower atmosphere where above 300$^0$ C it gradually decomposes into SO$_3$ and H$_2$O again.
SO$_3$ is then reduced by CO to SO$_2$ which can flow towards the equator and lift there again towards the clouds.

Question: Because the SO$_2$ that's lifting up from the lower atmosphere above the equator will become SO$_3$ mostly near the cloud top, will there not be a sulfuric acid free zone beneath the upper cloud deck there ?

This could be important for future missions to the atmosphere of Venus because within that sulfuric acid free zone would be the area, 50 to 60 km above the surface, with Earth-like temperatures and pressures.

  • $\begingroup$ I would not bet on it. Pictures of Venus such as this one show no evidence of a break in the sulfuric acid clouds around the equator. Sulfur trioxide could encounter and react with water vapor, thus completing the sulfuric acid formation process, before it could spread into a "zone" on either side of the equator. $\endgroup$ – Oscar Lanzi Aug 25 '19 at 19:00
  • $\begingroup$ @OscarLanzi The top of the acid free zone could be 10 km beneath the top of the cloud deck, for instance., so it could not be seen on pictures like that. The formation of sulfur trioxide can only happen when there are oxygen atoms available. $\endgroup$ – Cornelis Aug 25 '19 at 21:52
  • $\begingroup$ This questions seems to be requiring quite specific knowledge. Did you try and find some 2D or 3D chemical modeling papers of Venus? Those should exist. Otherwise mission reports from the global mapping by Venus Express, and their PFS instrument could help you... $\endgroup$ – AtmosphericPrisonEscape Aug 27 '19 at 0:27
  • $\begingroup$ @AtmosphericPrisonEscape I thought this is the site for such specific questions. An interested reader could give a great answer with some time consuming searching. As far as i know by now, there is much modelling with altitude but nothing such with latitude that could lead to an answer. $\endgroup$ – Cornelis Aug 27 '19 at 15:28

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