ISSI Proposal: The Atmosphere onVenus 8-9 Nov Proposal for an ISSI project Understanding the atmosphere of Venus Scientific background Lennart Bengtsson with Roger Bonnet and André Balogh

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Scientific rationale We need to better understand the atmosphere of Venus to demonstrate the generalities of models of planetary atmospheres presently mainly tested for the Earth. New observations from ESA Venus Express and soon from the Planet-C by Japan is setting a suitable time schedule. Venus is here a primary candidate as there are both similarities and considerable differences to the Earth We may be able to obtain further insight in the evolution of the Venus atmosphere. Has there been a greenhouse run-away effect on Venus? We may obtain further insight into the long-term future of the Earth if being exposed to massive greenhouse gases in the future.

ISSI Proposal: The Atmosphere onVenus 8-9 Nov What do the dynamical regimes of Venus and Earth have in common? What accounts for the differences in the atmospheric dynamics of these planets? Why study Venus’ atmospheric dynamics to understand the dynamics of Earth’s atmosphere?

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Major Dynamical Features of Earth’s Atmosphere Tropical Hadley cell confined to equatorial latitudes (  30  ). QBO Ferrel cells and polar cells. Subtropical jet stream. Large-scale baroclinic eddies in mid-latitudes. Thermal tides. Planetary waves. Mesopause over the equator is colder than over the winter pole. Seasonal variations. Major Dynamical Features of Venus’ Atmosphere Superrotation. Polar vortex. High latitude cloud level jet stream. Cloud level Hadley cell extending to polar latitudes? Thermal tides? Planetary waves. Mesospheric ( km) temperature increase from equator to the pole. Seasonal variations?

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Earth and Venus There may be more similarity between Earth and Venus than hitherto appreciated. Earth’s circulation is driven from below by solar heating variations. On Venus, solar heating is focused at cloud heights where T, p conditions are earthlike. The cloud level circulation on Venus might have some similar characteristics as circulation on Earth. Recent Venus GCM calculations by Sebastien Lebonnois suggest that atmospheric circulation is driven largely from above, at cloud levels, where solar heating is concentrated, with the lower massive atmosphere playing a more passive role. Earthlike features include a cloud level Hadley cell and high latitude jets.

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Lebonnois (2007)

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Earth and Venus The polar vortex on Venus may have some dynamical similarities to Earth’s hurricanes and stratospheric polar vortex. Pioneer Venus OIR image (1980) superimposed on Mariner 10 UV images (1974) Figure courtesy of Sanjay Limaye Venus Express VIRTIS UV and NIR images (2006) Downloaded from VEXP Web site

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Relevance for the Earth‘s climate in the longer perspective Is it a risk that there will be a run-away climate on the Earth? Probably not, as there are counteracting processes in the Earth’s atmosphere, such as clouds acting as a sort of thermostat and that heat is transported to higher latitudes where cooling is more efficient. But, we can not be sure as cloud distribution may change due to atmospheric circulation changes It can not be excluded that Venus has undergone a climate run away.

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Project Outline Three stage proposal Stage 1 Invite an expert group on the atmospheres of Venus and Earth to a meeting in ISSI with the purpose of defining/refining the scientific objectives of the elements of the project and to make concrete proposals for its scope and implementation. (First quarter 2008)

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Project Outline Three stage proposal Stage 2 Set up an ISSI Working Group on the scientific and technical aspects of modelling the atmospheres of Venus and Earth. This WG would review the status of Venus atmospheric models and the applicability of terrestrial models to Venus. It would also review the research currently carried out into modelling the Venus atmosphere and define/propose new methodologies. The output of the WG would be (a) a book in the ISSI Scientific Report Series and (b) technical and methodological input to the preparation of the Workshop outlined below. (The WG, of about 10 or so members, with ad hoc experts as appropriate would start their work in the first half of 2008, with a target duration of 1 year.)

ISSI Proposal: The Atmosphere onVenus 8-9 Nov Project Outline Three stage proposal Stage 3 Initiate an ISSI Workshop on the atmosphere of Venus, to be held in The main objective of such a workshop should be to summarize the knowledge situation and to explore how modelling and observational data could be suitably integrated. The expert group would advise on the detailed scope and contents of the Workshop and recommend a group of about five scientists to act as Convenors for the Workshop. It is proposed that the first meeting of the Convenors would take place in the 3 rd quarter of 2008.