1. Service d'Aéronomie du CNRS/IPSL, Verrières-le-Buisson 91371, France
2. Université Pierre et Marie Curie, 75252, Paris, France
3. Belgian Institute for Space Aeronomy, 3 avenue Circulaire, B-1180 Brussels, Belgium
4. Space Research Institute (IKI), 84/32 Profsoyuznaya, 117810 Moscow, Russia
5. Institut Pierre Simon Laplace, Université de Versailles-Saint-Quentin, 78 Saint-Quentin en Yvelines, 78280 Guyancourt , France
6. Faculty of Physics, Moscow State University, GSP-2 119992 Moscow, Russia
7. Moscow Institute of Physics and Technology, Institutsky dr. 141700 Dolgoprudny, Russia
8. Service d'Aéronomie du CNRS/IPSL, Verrières-le-Buisson 91371, France.
9. Belgian Institute for Space Aeronomy, 3 avenue Circulaire, B-1180 Brussels, Belgium.
10. Space Research Institute (IKI), 84/32 Profsoyuznaya, 117810 Moscow, Russia.
11. Laboratoire de Météorologie Dynamique, 4 place Jussieu, 75252 Paris cedex 05, France.
12. Max-Planck-Institut für Sonnensystemforschung Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau, Germany.
13. Southwest Research Institute, Department of Geophysics, Astrophysics and Planetary Science, 1050 Walnut Avenue, Suite 400, Boulder, Colorado 80302-5143, USA.
14. Groupe de Spectrométrie Moléculaire et Atmosphérique, Université de Reims, Champagne-Ardennes B.P. 1039, 51687 Reims cedex, France.
15. Université de Liège, Institut d'Astrophysique et Geophysique—B5c, Allée du 6 Aout, 17 Sart Tilman, B-4000 Liege, Belgium.
16. Lunar and Planetary Laboratory, University of Arizona, 1541 E. University Boulevard, Tucson, Arizona 85721, USA.

Correspondence to: Correspondence and requests for materials should be addressed to J.-L.B. (Email: bertaux@aerov.jussieu.fr).

Abstract

Venus has thick clouds of H₂SO₄ aerosol particles extending from altitudes of 40 to 60 km. The 60–100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar–antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside^{1, 2}. The mesosphere has a light haze of variable optical thickness, with CO, SO₂, HCl, HF, H₂O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90–120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H₂O and HDO. HCl is less abundant than reported 40 years ago³. HDO/H₂O is enhanced by a factor of 2.5 with respect to the lower atmosphere, and there is a general depletion of H₂O around 80–90 km for which we have no explanation.

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